If I stop, does it all come back?

Most of it, on the one trial that followed people properly. 327 adults who finished STEP 1 were followed for a further year with no drug and no lifestyle programme. They put back an average of 11.6 percentage points of the weight they had lost — about two-thirds of it — against 1.9 for the group that had been on dummy injections. A year after stopping they were still 5.6% below where they started. But the share still holding at least a 5% loss had fallen from 86.4% to 48.2%, and blood pressure, blood fats and blood sugar had drifted back too. A separate trial designed to test this directly, STEP 4, switched half the participants to a dummy injection at week 20. They gained 6.9% over the next 48 weeks, while those who carried on lost a further 7.9%.

Does it eat my muscle?

Some lean tissue does come off, and the marketing does not mention it. In a 140-person sub-group of STEP 1, scanned by X-ray at the start and at 68 weeks, fat mass fell 7.0 kg more than on dummy injections and belly-organ fat fell too. The regulator's assessors wrote that lean body weight also decreased, and decreased more than on dummy injections. But because fat came off so much faster, lean tissue made up a larger share of the body at the end — 2.94 percentage points more than on dummy injections. Their conclusion was that losing some lean weight is a usual part of any weight-loss programme. What nobody measured in that sub-study was strength, or what happens to that lean tissue in the year after someone stops.

Is it the same thing if I buy it online without a prescription?

No. Researchers identified 317 online pharmacies selling semaglutide and judged 134 of them to be operating illegally. They made test purchases from six. Three of the six never delivered anything and instead demanded a further 650 to 1,200 US dollars to clear customs. Of the three products that did arrive, all contained semaglutide, but at 29 to 39 per cent more than the label claimed. Purity came out between 7 and 14 per cent against an advertised 99 per cent, and one sample carried bacterial toxin at 8.95 endotoxin units per milligram. The researchers judged the products to be likely falsifications that do not meet legitimate quality standards.

Is it true that it makes you want to drink less?

There is one small randomised trial and it points that way, at amounts far below the ones used for weight. 48 adults with alcohol use disorder, none of them seeking treatment for their drinking, were given semaglutide or dummy injections for 9 weeks. In a laboratory drinking session those on semaglutide drank less alcohol by weight and reached a lower peak breath alcohol reading. Drinks per drinking day and weekly craving both fell. Among the 13 who smoked, cigarettes per day fell more. The authors themselves call it small and short. It does not say what happens at the amounts used for weight loss over a year.

Does it cause depression or suicidal thoughts?

The European regulator investigated exactly that. A review opened in July 2023 after case reports. At its meeting of 8 to 11 April 2024 the safety committee concluded that the available evidence does not support a causal link between these drugs and suicidal or self-harming thoughts and actions. The review covered laboratory studies, the trials, reports collected after the drugs went on sale, and two large studies of electronic health records, one run by the regulator itself. No change was made to the product information, and manufacturers were told to keep watching for it.

How real is the eye thing people are talking about?

Real, and very rare. On 6 June 2025 the European regulator's safety committee reached a conclusion about a sudden loss of vision in one eye, caused by the optic nerve losing its blood supply. It is a very rare side effect of Ozempic, Rybelsus and Wegovy. Very rare means it may affect up to 1 person in 10,000. The population studies it reviewed were in adults with type 2 diabetes and suggest roughly double the background risk, which works out at about one extra case per 10,000 person-years of treatment. There is no known window after starting when it is more likely, and the regulator's instruction is that the drug is stopped if it is confirmed. A separate and much more common eye problem is the worsening of existing diabetic eye damage. That happened in 3.0% against 1.8% over two years in 3,297 adults with type 2 diabetes, and is a different thing.

Metabolic

Semaglutide

Also known as Ozempic · Wegovy · Rybelsus · NN9535

Approved medicine

21 of 51 peptides sit at this level

Category: Metabolic
Doping status: Not banned in sport
Sources: 20
Trials: 1 trial · 1,961 people

Semaglutide is a laboratory-made copy of GLP-1, the gut hormone your body releases after a meal. It is rebuilt so it lasts about a week in the blood instead of a few minutes. It is an approved prescription medicine, sold as Ozempic and Rybelsus for type 2 diabetes and as Wegovy for weight management. The evidence behind it is unusually large: 1,961 adults over 68 weeks in the main weight trial, 17,604 adults over a median of 41.8 months in the heart trial. It reduces hunger, slows the stomach at first and lowers blood sugar. In people who already had heart disease it cut the number who had a heart attack, a stroke or died of a heart cause from 8.0% to 6.5%. It also makes about four in ten people feel sick. And a year after people stopped taking it in the trial extension, two-thirds of the weight they had lost was back.

SemaglutideTrials

Trials
What it is
Sold and legal
In your body
What changed
What can go wrong
Amounts studied
What people say
Unknowns
Questions
Sources

Weight-loss trials

1 trial · 2021

STEP 1 · 2021 · NEJM
Treatment-14.9 %
placebo-2.4 %
N
1 961
WEEKS
68
50.5% reached at least 15% weight loss, against 4.9% on placebo.
[source] — STEP 1, NEJM 2021

What it is

A synthetic version of the gut hormone GLP-1. It is approved in the EU under three names: Ozempic and Rybelsus for type 2 diabetes, and Wegovy for weight management.

How it is sold, and whether it is legal

Sold as: Injection under the skin (Ozempic, Wegovy); tablet (Rybelsus).
Legal status in the EU: Approved by the European regulator: Ozempic on 8 February 2018, Rybelsus on 3 April 2020 and Wegovy on 6 January 2022 (all Novo Nordisk A/S). Prescription only. In July 2024 the regulator refused a separate heart-protection indication for Wegovy on the grounds that the use was already covered by the approved weight management indication, and instead added the SELECT data to the product information. Semaglutide does not appear on the 2026 WADA list.

What it does in your body

6 parts of the body · all measured in people

Semaglutide switches on the GLP-1 receptor, which releases insulin only when blood sugar is high, reduces the hormone that raises blood sugar, slows how fast the stomach empties, and reduces appetite. According to Lau and colleagues (2015) the molecule has two amino acid swaps compared with human GLP-1 and a modification at position 26, which makes it stick to a blood protein and last a week. The sequence is left empty because one of the substituted building blocks is outside the standard set and cannot be written correctly in one-letter code.

Appetite, in the brain: This is the effect people notice first and describe most. The docking points GLP-1 uses sit in the parts of the brain that decide how hungry you are; animal work is what shows semaglutide acting on those parts directly. What was measured in people is simpler: they eat less, feel full sooner, and feel hungry less often. People describe wanting less rather than resisting more. The effect on savoury cravings is clearer than the effect on sweet cravings.; Energy intake measured directly at an eat-as-much-as-you-like meal in an early-stage trial after 20 weeks of dosing: 35% less food eaten than on a dummy injection. Cravings were measured by questionnaire in 304 adults over 104 weeks in STEP 5. There, control of cravings and craving for savoury food both favoured semaglutide, and craving for sweet food showed no clear effect.; Measured in people; Source [11]
Stomach and gut: The second thing people notice, and the reason most of those who stop, stop. Feeling sick, being sick, loose stools and constipation all appear mainly in the early weeks while the amount is still being built up, and most of them pass. Constipation is the exception: it lasts far longer than the others. The stomach also empties more slowly at first, but the body adapts to that part. The regulator states that at the 2.4 mg weekly amount there was no longer any meaningful slowing of stomach emptying, probably because tolerance develops.; Counted in 2,650 adults across four 68-week trials: feeling sick in 43.9% against 16.1% on dummy injections, diarrhoea in 29.7% against 15.9%, vomiting in 24.5% against 6.3%, constipation in 24.2% against 11.1%. Median duration in those who had it: 8 days for nausea, 2 days for vomiting, 3 days for diarrhoea and 47 days for constipation. Gut symptoms led 4.3% to stop the drug for good.; Measured in people; Source [11]
Body fat and muscle: Most of what comes off is fat. That includes the fat packed around the organs inside the belly, which is the kind linked to heart and metabolic disease. Muscle and other lean tissue come off too. The regulator's assessors put it plainly: lean body weight decreased more on semaglutide than on dummy injections. But because fat fell so much faster, lean tissue made up a larger share of the body at the end than at the start. Losing some lean tissue is what happens in any substantial weight loss, drug or no drug.; Body composition scanned by X-ray in a 140-person sub-group of STEP 1, at the start and at 68 weeks. Total fat mass fell 7.0 kg more than on dummy injections — the study could narrow that figure only to somewhere between 4.2 and 9.8 kg — and belly-organ fat by 0.3 kg more. As a share of body weight, lean mass rose 2.94 percentage points more than on dummy injections, in a range from 1.40 to 4.49. A second sub-group of 55 people was scanned by MRI in STEP UP over 72 weeks with the same pattern.; Measured in people; Source [11]Source [12]
Blood sugar and the pancreas: Semaglutide tells the pancreas to release insulin, the hormone that pulls sugar out of the blood. It does this only when blood sugar is high, which is why it does not normally cause the low-blood-sugar crashes that insulin injections can. It also turns down glucagon, the hormone that pushes sugar into the blood. In people whose blood sugar was already drifting upwards, this is often enough to bring it back into the normal range. In a small number of people the pancreas becomes inflamed, which is painful and can put someone in hospital.; In STEP 1, 84.1% of the participants who started with prediabetes — blood sugar above normal but not yet diabetes — had normal blood sugar at 68 weeks, against 47.8% on dummy injections. In 1,210 adults with type 2 diabetes over 68 weeks (STEP 2), long-term blood sugar fell by 1.6 percentage points against 0.4 on dummy injections. Inflammation of the pancreas confirmed by an independent panel occurred in 0.2% on semaglutide and under 0.1% on dummy injections across the four 68-week trials. In the 17,604-person heart trial it was 0.2% against 0.3%.; Measured in people; Source [11]
Heart and blood vessels: Blood pressure falls. In people who already had heart disease, fewer of them went on to have a heart attack, a stroke or to die of a heart cause. The resting pulse goes the other way — it speeds up slightly and stays up. The regulator is explicit that nobody has established why the heart benefit happens. Weight, blood pressure, blood fats, blood sugar and inflammation all improved at once, and the trial cannot separate them.; Measured in 17,604 adults with existing heart disease and a body mass index of 27 or above, followed for a median of 41.8 months (SELECT). The top blood pressure number fell 6.2 mmHg against 1.1 on dummy injections in STEP 1's 1,961 adults. Resting pulse rose by an average of 3 beats a minute from a starting average of 72 across the four 68-week trials. A rise of 10 beats or more at some point was seen in 67.0% on semaglutide against 50.1% on dummy injections.; Measured in people; Source [11]
Eyes: Two separate things, and they get confused with each other. The first: in people who already have damage to the small blood vessels at the back of the eye from diabetes, bringing blood sugar down quickly can make that damage temporarily worse. The second, and newer: a sudden loss of vision in one eye caused by the optic nerve losing its blood supply. The European regulator reviewed this in 2025 and concluded it is a real but very rare side effect. The product information states there is no known window of time after starting when it is more likely.; Eye damage from diabetes was counted in a two-year trial of 3,297 adults with type 2 diabetes, high heart risk and poorly controlled blood sugar. Complications occurred in 3.0% on semaglutide against 1.8% on dummy injections, concentrated in people already on insulin who already had eye damage. For the optic nerve condition, the regulator's safety committee reviewed several large population studies in adults with type 2 diabetes. Those suggest roughly double the relative risk, which works out at about one extra case per 10,000 person-years of treatment.; Measured in people; Source [09]Source [11]

What changed when it was measured

12 findings · 11 measured in people, 1 from one small study

STEP 1 (NEJM 2021, 1,961 participants, 68 weeks) gave −14.9% body weight versus −2.4% for placebo; 50.5% versus 4.9% lost at least 15%. SELECT (NEJM 2023, 17,604 participants, followed for an average of 39.8 months) showed the main heart outcome in 6.5% versus 8.0% (hazard ratio 0.80; 95% CI 0.72–0.90). SUSTAIN-6 (NEJM 2016, 104 weeks) showed a hazard ratio of 0.74 (95% CI 0.58–0.95) for heart events, but at the same time 1.76 (95% CI 1.11–2.78) for eye complications.

Slow to arrive and slow to leave. Semaglutide sticks to a blood protein, which is why one injection lasts a week. After the last injection it is still in the blood for about seven weeks. The regulator's own summary of the weight trials is that weight loss occurred early and continued throughout. In the two-year trial the curve flattened around week 68 and then stayed flat, so most of what a person is going to lose has gone by about fifteen months. The gut effects run on a much shorter clock and appear mainly in the early weeks, while the amount is still being built up. The middle case of nausea lasted 8 days, vomiting 2 days and diarrhoea 3 days. Constipation is the outlier at 47 days. The stomach's slowing is temporary in a way the appetite effect is not. The regulator states that at the 2.4 mg weekly amount there was no longer any meaningful delay in stomach emptying, probably because the body adapts to that part. Going the other way, the STEP 1 extension followed 327 people for a year after everything stopped. Two-thirds of the lost weight was back, and blood pressure, blood fats and blood sugar had drifted back with it.

Body weight: Weight fell 14.9% against 2.4% on a dummy injection — 15.3 kg against 2.6 kg. At least 5% of body weight was lost by 83.5% against 31.1%, at least 10% by 66.1% against 12.0%, and at least 15% by 47.9% against 4.8%. Waist measurement fell 13.5 cm against 4.1 cm.; 1,961 adults with obesity, or overweight plus a weight-related health problem, no diabetes, 68 weeks; everyone in both groups was also put on a reduced-calorie diet and more activity; Measured in people; Source [11]
What happened after people stopped taking it: The drug and the lifestyle programme were both withdrawn. Over the following year the semaglutide group put back an average of 11.6 percentage points of the weight they had lost, against 1.9 in the group that had been on dummy injections. That is about two-thirds of what they had lost. At the end of that year they were still 5.6% below where they started, against 0.1% for the dummy group. The share still holding at least a 5% loss fell from 86.4% to 48.2%. Blood pressure, blood fats, inflammation and long-term blood sugar all drifted back towards where they had started.; 327 adults who completed the 68-week STEP 1 trial and were then followed for a further 52 weeks with no treatment at all; Measured in people; Source [11]Source [13]
Carrying on versus being switched to a dummy injection part-way through: Everyone took semaglutide for the first 20 weeks. Those kept on it lost a further 7.9% over the next 48 weeks. Those switched to a dummy injection gained 6.9% back over the same 48 weeks — a gap of 14.8 percentage points. The switched group still weighed less at the end than at the very beginning.; 902 adults with obesity or overweight plus a weight-related health problem; 803 of them reached the maintenance amount at week 20 and were randomised at that point, 48 further weeks; Measured in people; Source [11]
Heart attacks, strokes and deaths from heart causes: 569 of 8,803 people on semaglutide had one of these (6.5%) against 701 of 8,801 on dummy injections (8.0%). That is a hazard ratio of 0.80, meaning a fifth fewer. Heart attacks that were not fatal: 234 against 322 (hazard ratio 0.72). Strokes that were not fatal: 154 against 165 (hazard ratio 0.93, a range that includes no difference at all). Deaths from any cause: 375 against 458.; 17,604 adults with established heart disease and a body mass index of 27 or above, no diabetes, median 41.8 months; Measured in people; Source [02]Source [11]
Kidney decline in people with type 2 diabetes and existing kidney damage: A combined measure counted losing half of kidney function, reaching kidney failure, starting dialysis or a transplant, dying of kidney disease, or dying of a heart cause. It happened to 331 of 1,767 people on semaglutide against 410 of 1,766 on dummy injections — a hazard ratio of 0.76, meaning about a quarter fewer. Kidney function declined more slowly by 1.16 mL/min/1.73m2 a year. Deaths from any cause fell too. The trial was stopped early because the benefit was already clear.; 3,533 adults with type 2 diabetes and chronic kidney disease, average age 66.6 years, median follow-up 40.9 months; Measured in people; Source [14]
Long-term blood sugar and weight in people who also have type 2 diabetes: Long-term blood sugar fell 1.6 percentage points against 0.4 on dummy injections. Weight fell 9.6% against 3.4% — noticeably less than the 14.9% seen in people without diabetes. At least 15% of body weight was lost by 25.0% against 4.3%.; 1,210 adults with overweight or obesity and insufficiently controlled type 2 diabetes, 68 weeks; Measured in people; Source [11]
Two years rather than one: Weight fell 15.2% against 2.6% on dummy injections. The curve flattened out around week 68 and stayed flat for the remaining 36 weeks. The weight loss did not continue indefinitely, and it did not reverse while treatment continued.; 304 adults with obesity or overweight plus a weight-related health problem, 104 weeks; Measured in people; Source [11]
A higher weekly amount against the standard one: Weight fell 18.7% on the 7.2 mg amount, 15.6% on the standard 2.4 mg amount and 3.9% on dummy injections. The higher amount beat the standard one by 3.1 percentage points. At least 25% of body weight was lost by 31.2% of the higher-amount group, against 15.3% on the standard amount and nobody at all on dummy injections. The cost showed up in the skin. Odd or painful skin sensations were reported by 21.6% on 7.2 mg against 0.3% on dummy injections, and hair loss by 5.3% against 1.0%.; 1,407 adults with obesity in STEP UP, 72 weeks; a companion trial of 514 adults with obesity and type 2 diabetes ran alongside it; Measured in people; Source [11]
Against the older daily injection: Weight fell 15.8% on weekly semaglutide against 6.4% on liraglutide, an injection taken every day rather than every week. At least 20% of body weight was lost by 37.4% against 7.0%. More people stopped the daily injection than the weekly one: 27.6% against 13.5%.; 338 adults with obesity or overweight plus a weight-related health problem, randomised to weekly semaglutide, daily liraglutide or dummy injections, 68 weeks; 126 and 127 in the two active groups analysed; Measured in people; Source [11]
Breathlessness and how far people could walk, in a type of heart failure caused by obesity: A symptom score out of 100 rose 16.6 points against 8.7 on dummy injections. Distance walked in six minutes rose 21.5 metres against 1.2 metres. In the companion trial in people who also had type 2 diabetes the gains were smaller but in the same direction: 13.7 against 6.4 points, and 12.7 metres against a loss of 1.6 metres.; 529 adults with obesity-related heart failure with a preserved pumping fraction, and 616 adults with the same condition plus type 2 diabetes, average age 68, 52 weeks; Measured in people; Source [11]
Knee pain in people with worn knee joints: A pain score out of 100 improved by 41.7 points against 27.5 on dummy injections. Weight fell 13.7% against 3.2%. The pain improvement happened without people taking more painkillers.; 407 adults with obesity and moderate wear in one or both knees, average body mass index 40.3, 68 weeks; Measured in people; Source [11]
How much alcohol people drank: In a laboratory drinking session, people on semaglutide drank less alcohol by weight than those on dummy injections. They also reached a lower peak breath alcohol reading. Drinks per drinking day fell, and so did weekly craving. Among the 13 people in the trial who smoked, cigarettes per day fell more on semaglutide. This was a small, short, early-stage trial. It used far lower amounts than the weight-management ones, and the people in it were not seeking treatment for their drinking.; 48 adults with alcohol use disorder, 34 of them women, average age 39.9, 9 weeks; One small study; Source [15]

What can go wrong

17 effects, 9 serious

Nausea, vomiting, diarrhoea, constipation, abdominal pain and headache affect more than 1 in 10. In SELECT, 16.6% stopped treatment because of side effects versus 8.2% in the placebo group. On 6 June 2025 the European regulator's safety committee classified the eye condition NAION as a very rare side effect (up to 1 in 10,000); gallbladder disease and pancreatitis are known risks across the class.

An inflamed pancreasSerious: Severe pain high in the belly that often bores through to the back, usually with vomiting. It is the kind of thing people go to hospital for. The regulator's instruction is that the drug is stopped if it is suspected and never restarted if it is confirmed. In the 17,604-person heart trial the rates were 0.2% on semaglutide and 0.3% on dummy injections — no signal at all in the largest study.; Uncommon — between 1 and 10 people in every 1,000. Confirmed by an independent panel in 0.2% on semaglutide against under 0.1% on dummy injections across the four 68-week trials.; Source [11]
Gallstones and an inflamed gallbladderSerious: Losing weight quickly makes gallstones more likely whatever causes the weight loss. They can sit silently for years or they can block the bile duct, which is an emergency. This is the one side effect where the adolescent rate came out higher than the adult rate.; Gallstones in 1.6% on semaglutide against 1.1% on dummy injections; the gallbladder became inflamed in 0.6% against 0.3%. In the trial in 12- to 17-year-olds, gallstones were reported in 3.8% on semaglutide and none on dummy injections.; Source [11]
Sudden loss of vision in one eyeSerious: The optic nerve loses its blood supply and vision in that eye goes, usually painlessly and usually on waking. It is often permanent. The European regulator's safety committee added it to the product information for Ozempic, Rybelsus and Wegovy on 6 June 2025. There is no known point after starting when it is more likely to happen.; Very rare — fewer than 1 person in 10,000. The population studies the regulator assessed were in adults with type 2 diabetes and put it at roughly double the background risk, which works out at about one extra case per 10,000 person-years of treatment.; Source [09]Source [11]
Worsening eye damage in people who already have it from diabetesSerious: It happened in people already on insulin who already had damage to the small vessels at the back of the eye. The difference appeared early and did not go away. The regulator notes that bringing blood sugar down fast is itself known to cause a temporary worsening, so the drug and the improvement it causes cannot be fully separated. Semaglutide is not recommended at all for people with type 2 diabetes whose eye disease is unstable.; 3.0% against 1.8% on dummy injections over two years in 3,297 adults with type 2 diabetes. In the 68-week trial in people with diabetes, retinal problems were reported by 6.9% on the weight-management amount against 4.2% on dummy injections.; Source [11]
A blocked bowelSerious: The gut stops moving things along. It presents as a swollen, painful belly with vomiting and no bowel movement, and it is a surgical emergency. A 2023 study of insurance records compared people prescribed a GLP-1 drug for weight loss against people prescribed a different weight-loss drug. It found roughly four times the rate of bowel obstruction, in a range so wide it ran from barely any difference to seventeen times. Of the 4,757 GLP-1 users in that study only 613 were on semaglutide, and none of those 613 had a bowel obstruction. Every one of the 73 events was in the liraglutide group.; Frequency not known — the regulator lists it with no rate that can be calculated from the available data.; Source [11]Source [16]
Stomach contents going into the lungs during an operationSerious: Because the drug slows the stomach, food can still be sitting there when someone is put to sleep for an operation or a scope. It can then go down the wrong way into the lungs. It is a warning about a procedure, not something that happens in daily life.; Reported cases; no rate published. The regulator added it as a warning rather than a counted side effect.; Source [11]
A whole-body allergic reactionSerious: The kind of reaction that drops blood pressure and closes the airway. A previous allergic reaction to semaglutide or to anything else in the injection is the single thing the European product information lists as an outright bar to taking it.; Rare — between 1 and 10 people in every 10,000. Swelling of the face, lips or throat is listed as rare too.; Source [11]
Blood sugar dropping too lowSerious: This is not much of a risk for people taking it for weight alone, because the drug only releases insulin when blood sugar is already high. It becomes a real risk alongside insulin or a sulfonylurea, an older diabetes tablet, because those lower blood sugar regardless. Shakiness, sweating, confusion; the severe kind needs someone else's help.; 6.2% against 2.5% on dummy injections in the 1,210-person trial in people with type 2 diabetes. One episode, in 0.2% of that group, was severe.; Source [11]
Kidney function getting worse through dehydrationSerious: Being sick and having diarrhoea for days dries a person out, and dried-out kidneys work badly. It matters most for people whose kidneys already work poorly, and the regulator notes those people also get more gut symptoms in the first place.; Rare, and a consequence of the vomiting and diarrhoea rather than a direct effect on the kidney.; Source [11]
Feeling sick: The single most common thing that happens. It clusters in the early weeks while the amount is being built up, most cases were mild to moderate, and the middle case lasted 8 days. It is also the thing people most often describe as the price of the drug working.; About 4 in 10 — 43.9% against 16.1% on dummy injections, across 2,650 adults in four 68-week trials.; Source [11]
Diarrhoea: Mostly mild to moderate and short — the middle case lasted 3 days. People with moderately reduced kidney function get more of it.; 29.7% against 15.9% on dummy injections.; Source [11]
Being sick: Nearly four times the rate on dummy injections, and the shortest-lived of the gut effects — the middle case lasted 2 days. It is the one most likely to cause dehydration if it goes on.; 24.5% against 6.3% on dummy injections.; Source [11]
Constipation: The gut effect that does not pass quickly. The middle case lasted 47 days — nearly six times longer than nausea. The regulator describes it as mild to moderate but of longer duration, which is a mild way of saying seven weeks.; 24.2% against 11.1% on dummy injections.; Source [11]
Belly pain, headache and tiredness: Headache, dizziness, a metallic or altered taste and tiredness are all recorded as things that show up mainly while the amount is being built up.; All in the very common band — more than 1 person in 10. In the US label's table: belly pain 20% against 10%, headache 14% against 10%, tiredness 11% against 5%.; Source [11]Source [17]
Hair loss: Mostly mild, and most people's hair recovered while they carried on taking the drug. The regulator notes it was reported more often by people who had lost 20% or more of their body weight. That points at the speed of the weight loss as much as at the drug.; 2.5% against 1.0% on dummy injections at the standard amount; 5.3% against 1.0% at the higher 7.2 mg amount.; Source [11]
Odd, burning or painful skin sensations: Pins and needles, skin that hurts to touch, a burning feeling. Mild to moderate in most cases, and 85% of the events at the higher amount settled while people stayed on the drug. This is the clearest example in the whole record of a side effect that barely exists at one amount and is common at another.; 2.1% against 1.2% on dummy injections at the standard amount. At the higher 7.2 mg amount it was 21.6% against 0.3% — one person in five.; Source [11]
A faster resting pulse: Most people never notice it. It is listed as a common side effect and it does not go away with time on the drug, unlike the gut effects.; An average rise of 3 beats a minute from a starting average of 72. A rise of 10 beats or more at some point was seen in 67.0% on semaglutide against 50.1% on dummy injections.; Source [11]

Who it is known to be dangerous for

The European product information lists only one outright bar: a previous allergic reaction to semaglutide or anything else in the injection. The US label goes further. It forbids the drug outright for anyone with a personal or family history of medullary thyroid cancer, or of the inherited condition MEN 2. The reason is that in rats and mice semaglutide caused thyroid tumours at exposures comparable to human ones. The European regulator adds that the relevance of that finding to people is considered low, but cannot be ruled out. In pregnancy the European regulator says it should not be used at all. Because it lingers for weeks, it should be stopped at least two months before someone tries to conceive. It should not be used while breastfeeding either. It is not recommended for people with type 1 diabetes, severe kidney impairment or severe liver impairment. Nor for people with the most severe class of heart failure, unstable eye damage from diabetes, or severe gastroparesis — a stomach that already empties too slowly. It is not to be combined with another GLP-1 drug or with other weight-management medicines, because that has never been tested. Caution is advised for people aged 85 or older, people with milder liver impairment, and people with inflammatory bowel disease, all of whom are barely represented in the trials. Anyone also taking insulin or a sulfonylurea has a higher risk of blood sugar dropping too low. Anyone on warfarin or a similar blood thinner needs their clotting checked more often when starting, because cases of blood clotting more readily have been reported with a closely related medicine.

The amounts the studies used

11 amounts

These are the amounts the studies below gave their participants, and they are here as facts about those studies. They are not a recommendation, not a starting point and not a range to pick from. What a person should take, if anything, is a question for a doctor who knows them.

STEP 1, weight in 1,961 adults with obesity and no diabetes: 2.4 mg once a week, injected under the skin; 68 weeks; Source [11]
SELECT, heart attacks and strokes in 17,604 adults with existing heart disease: 2.4 mg once a week, injected under the skin; Median 41.8 months; Source [11]
STEP 5, the two-year weight trial in 304 adults: 2.4 mg once a week, injected under the skin; 104 weeks; Source [11]
STEP UP, the higher-amount trial in 1,407 adults with obesity, which also had a 2.4 mg group and a dummy group: 7.2 mg once a week, injected under the skin; 72 weeks; Source [11]
STEP-HFpEF, breathlessness and walking distance in 529 adults with obesity-related heart failure: 2.4 mg once a week, injected under the skin; 52 weeks; Source [11]
STEP 9, knee pain in 407 adults with obesity and worn knee joints: 2.4 mg once a week, injected under the skin; 68 weeks; Source [11]
SUSTAIN 6, the heart-outcomes trial in 3,297 adults with type 2 diabetes, run at the lower diabetes amounts: 0.5 mg or 1 mg once a week, injected under the skin; 104 weeks; Source [11]
FLOW, kidney decline in 3,533 adults with type 2 diabetes and chronic kidney disease: 1 mg once a week, injected under the skin; Median 40.9 months; the trial was stopped early for benefit; Source [14]
PIONEER 1, the tablet form on its own in 703 adults with type 2 diabetes, against dummy tablets: 3 mg, 7 mg or 14 mg once a day, swallowed; 26 weeks; Source [18]
PIONEER PLUS, the higher tablet amounts in 1,606 adults with type 2 diabetes already on other diabetes tablets, with no dummy group: 14 mg, 25 mg or 50 mg once a day, swallowed; 68 weeks; Source [18]
The alcohol trial in 48 adults with alcohol use disorder, which built up to an amount far below the weight-management ones: 0.5 mg once a week, injected under the skin; 9 weeks; Source [15]

What people report

What follows is what people say online. It is not evidence, it is not graded, and it is not checked by anyone. People who had a bad time and people who are selling something both post more than people for whom nothing happened. It is here because you would go and read it anyway, and knowing who is talking is better than not.

The constant background noise about food goes quiet

This is the thing people volunteer first, ahead of the weight. Thirty people taking GLP-1 drugs across 15 US states were interviewed in depth, and the strongest theme was a drop in what they called food noise. One described how her whole world had been around food, and how being clear-headed changed what she reached for when she felt low. A review of nine studies of patient experience found the same, with people describing sharply reduced cravings for sweet things in particular.

Read in A 30-person interview study published in JAMA Network Open in 2026, and a 2025 systematic review of nine studies of patients' experiences with GLP-1 drugs