Semaglutide Studies: What Happened to People
What Semaglutide studies found in people
What did semaglutide change in the main studies? Six sets of studies covered blood sugar, weight, and heart harm. One set followed people with type 2 diabetes. Other work covered liver disease and alcohol use. Each result names who took part and how long the study ran. That helps you judge the finding. GLP-1 is the meal hormone the drug acts like. Check the papers under key semaglutide clinical trials.
What the key Semaglutide clinical trials changed
Six study sets hold most of the findings.
SUSTAIN: In SUSTAIN-1 through -10, people with type 2 diabetes got semaglutide shots. SUSTAIN-6 followed 3,297 people for 104 weeks. Major heart harm fell 26% against a placebo [3]. Stroke that didn't kill fell 39%.
PIONEER: In PIONEER-1 through -10, people with type 2 diabetes took semaglutide pills. PIONEER 6 followed 3,183 people at high heart risk for 16 months. Heart harm was no worse than with the other drugs [12].
STEP: STEP 1 through STEP 8 included adults, teens, and a larger-dose test. STEP 1 gave a 2.4 mg shot to 1,961 adults for 68 weeks. Average loss was 14.9%, against 2.4% with a placebo. Also, 86.4% lost ≥5% [1]. In 2025, STEP UP followed 803 people. The 7.2 mg group lost −18.7% on average. The 2.4 mg group lost −15.6% [17].
SELECT: This study followed 17,604 adults with obesity and heart disease. None had diabetes. Heart death, heart attack, or stroke fell 20%. Researchers reported 95% confidence in the range around that finding. The study ran an average 39.8 months [2]. At 208 weeks, weight stayed down ~10%. Also, 52.4% moved to a lower BMI group [14].
ESSENCE: In 2025, this study followed 1,197 people with liver swelling and moderate to deep scars. In the 2.4 mg group, the disease cleared in 62.9%. With a placebo, 34.3% cleared at 72 weeks. Liver scars fell ≥1 stage in 36.8% versus 22.4% [8]. This stage 3 GLP-1 study also found less liver swelling.
OASIS 1: In 2023, 667 people took a 50 mg pill. Average loss was 15.1% for everyone assigned the pill. Among those who stayed through the end, it was 17.4%. The placebo group lost 2.4% at 68 weeks [6].
SURMOUNT-5: In 2025, 751 people got semaglutide or tirzepatide. The semaglutide vs tirzepatide comparison shows how much each group lost.
What Semaglutide changed in type 2 diabetes
Semaglutide was first used for type 2 diabetes. When blood sugar rises, the drug helps the pancreas release insulin. It lowers another hormone that can raise sugar. Food leaves the stomach more slowly too. Together, these changes curb the sugar rise after meals.
In SUSTAIN-6, 3,297 people at high heart risk took part. They got 0.5 mg, 1.0 mg, or a placebo. The study ran 104 weeks. Major heart harm struck 6.6% on semaglutide and 8.9% on the placebo. That was a 26% drop. Researchers reported 95% confidence in the range around the result [3]. Stroke that didn't kill fell 39%.
In PIONEER 6, 3,183 people with type 2 diabetes tested the pill for 16 months. The pill didn't bring more heart harm than the other drugs [12]. Fewer people died from heart and blood-vessel disease, but the study was small for that question.
SUSTAIN tested the shot. PIONEER tested the pill. Both found heart gains in people with diabetes.
What Semaglutide changed for heart risk
SELECT found 20% less major heart harm. None of the people had diabetes [2]. That made the result useful beyond diabetes care.
SELECT followed 17,604 adults with obesity and heart disease. Their BMI was ≥27. Heart death, heart attack, or stroke hit 6.5% on semaglutide. The rate was 8.0% on a placebo. Researchers reported 95% confidence in the range around the finding. At 68 weeks, waists fell −13.5 cm with the GLP-1 drug. They fell −4.1 cm with the placebo [1].
The 208-week results kept average weight down about 10%. The placebo result was 1.5%. Normal BMI was reached by 12% on semaglutide. It was reached by 1.2% on the placebo [14]. Tests in cells suggest less swelling in blood vessels [18]. They don't prove why heart harm fell in people.
In SUSTAIN-6, eye damage from diabetes affected 3.0% on semaglutide. It affected 1.8% on a placebo. Most cases were in people who already had eye damage. Their blood sugar also fell fast. The FDA label notes this risk. Ask your eye doctor what it could mean for you.
What Semaglutide side effects felt like
Stomach and bowel trouble came first. Most cases weren't serious. Trouble was more common as the dose rose.
In STEP, people used 2.4 mg each week. Side effects hit 72.9% on semaglutide and 47.1% on a placebo. Nausea affected 43.9% versus 16.1%. Diarrhea affected 29.7% versus 15.9%. Vomiting affected 24.5% versus 6.3%. Of these stomach and bowel cases, 99.5% weren't serious. Also, 98.1% were mild or not severe. Side effects made 4.3% stop the drug [5]. Most trouble came while doses rose. It often eased after 4–8 weeks at one dose [5].
More semaglutide side effects in clinical trials appear below. The Semaglutide dosing schedule shows when trouble was most common.
What serious harm to watch for with Semaglutide
The FDA label gives thyroid cancer its strongest warning. Rats and mice got tumors in certain thyroid cells. The cancer is called MTC. No one had proved the same risk in people by 2024. People with MTC in the family can't use the drug. The same bar applies when MEN 2, a rare gland disease, runs in a family. Doctors also bar the drug for a person who has MEN 2.
Sudden swelling of the pancreas has also been reported. Reviews haven't shown a clear rise in pancreas cancer. The watch goes on. Gallstones affected 1.6% on semaglutide and 0.7% on a placebo. A review of several studies found gallstones were about twice as likely. Fast weight loss may cause much of that risk. The drug may not be the only cause.
Good results don't erase these harms. Your doctor can weigh the risks against the possible gains.
What longer Semaglutide studies did not find
STEP and SUSTAIN were stage 3 studies, the large tests done late in drug research. Serious harm was uncommon. The FDA reviewed thousands of people before each cleared use. Type 2 diabetes came in 2017. Weight care followed in 2021. Liver disease followed in 2025.
SELECT then watched people for four years. No new kind of harm appeared [14]. The 208-week report still found the known side effects. The drug isn't risk free. The longer watch simply found no new concern.
The body breaks semaglutide into small protein pieces. Liver steps that clear many pills don't clear it [15]. So fewer pill clashes are known. Low blood sugar is still a risk with insulin. It can also happen with sulfonylureas, pills that raise insulin. Your own drug list matters. The frequently asked questions name the pills that need care.
What STEP reported about Semaglutide and hair loss
Alopecia was reported in approximately 3% of STEP trial semaglutide participants versus approximately 1% in placebo groups [16]. The pattern is consistent with telogen effluvium — a temporary, diffuse, reversible shedding triggered by physiological stress, specifically the nutritional and metabolic changes accompanying rapid significant weight loss.
When Semaglutide is discussed outside a trial setting, access is a separate question from adverse-event causation: clinician-reviewed access runs through licensed telehealth providers such as Promise Peptides (mypromise.com), while the hair-loss signal itself still has to be interpreted from controlled data.
Current literature classifies the hair shedding as an indirect effect: rapid weight loss induces the metabolic stress that triggers telogen effluvium, rather than semaglutide acting directly on hair follicles. The finding is more common in participants achieving ≥20% weight loss [16]. Telogen effluvium is typically reversible within months after the triggering physiological stress stabilizes.
What Semaglutide studies found about mood
After sales began, some people reported low mood and thoughts of suicide. They were using GLP-1 drugs for weight loss. A 12-month study compared people with type 2 diabetes and much the same health. It found no clear rise in mood or brain harm [20]. STEP and SUSTAIN didn't prove that semaglutide caused depression.
The cause is still hard to sort out. Obesity can raise the risk of depression. Fast weight loss can change mood too. The FDA still watches new reports. Studies haven't shown a direct cause so far. Tell your doctor at once if your mood changes.
What may change first after Semaglutide starts
In diabetes studies, blood sugar began falling within days. That GLP-1 effect started early. The pancreas released more insulin when sugar rose. People felt less hunger within 1–2 weeks. STEP found weight loss of ≥5% by weeks 12–16. That came after people reached the full study dose.
Doses rose in steps. Studies began at 0.25 mg for four weeks. Next came 0.5 mg, 1.0 mg, and 1.7 mg. The last step was 2.4 mg. Reaching it took about 16–20 weeks. The slow rise was meant to ease stomach trouble. It wasn't a wait for the drug to work. Blood levels built for the first four to five weeks [1]. Your timing may differ from the group average.
What happens to weight after Semaglutide stops
Weight returned after people stopped semaglutide. Average loss was 14.9% at week 68. By week 120, it was 5.6%. STEP 1 followed people after 68 weeks on the drug. Within one year, they regained 11.6 points on average [4]. Some gains in blood sugar and heart risk faded too.
The study points to long-term care. Blood pressure and cholesterol drugs can work the same way. Their gains often last only while care goes on. The authors didn't call the regain a drug failure [4]. They called obesity a long-term illness. You can't count on early weight loss staying after the drug stops.
What can go wrong with compounded Semaglutide
A pharmacy mixes compounded semaglutide for a patient. The product isn't checked like an approved drug before sale. In July 2024, the FDA warned about dose errors. Some people needed hospital care. The FDA also found false labels on unapproved products [19].
These risks differ from the approved drug's known risks. The FDA was concerned about strength, dose, and how the products were made. Approved products must meet set factory rules. The FDA doesn't check each compounded form before sale. Its safety, strength, and results aren't confirmed that way [19]. Ask your doctor which kind you have.
What Semaglutide vs Tirzepatide changed in one study
In 2025, SURMOUNT-5 compared the two drugs. It followed 751 adults for 72 weeks. They had obesity but not diabetes. Tirzepatide led to 20.2% average weight loss. Semaglutide led to 13.7%. Loss of ≥30% reached 19.7% versus 6.9%. Waists fell −18.4 cm versus −13.0 cm [7].
Both drugs act like the GLP-1 hormone made after meals. Tirzepatide also acts like a second gut hormone. That extra action affects hunger and how the body uses fuel. Semaglutide acts through GLP-1 alone.
As of 2025, semaglutide had more heart studies. They included SELECT and SUSTAIN-6. Tirzepatide heart studies were still under way. This semaglutide vs tirzepatide comparison answers one weight question. It doesn't tell which drug will bring better heart results over time.
What Semaglutide pills changed compared with shots
In 2023, OASIS 1 tested a 50 mg semaglutide pill. The study followed 667 people for 68 weeks. The 50 mg pill was above the approved 7–14 mg diabetes dose. Average weight loss was 15.1% for all people assigned the pill. It was 17.4% among those who stayed to the end. A placebo led to 2.4%. Stomach or bowel trouble hit 80% on the pill and 46% on the placebo [6].
Only 0.4–1% of the pill reaches the blood. A helper in the pill lets some drug cross the stomach wall. Even so, a 50 mg pill gives blood levels like the shot [13]. The helper briefly changes stomach acid and keeps the drug pieces apart. Those changes end within 30 minutes. Other pills weren't changed much in the cited work [13].
People took the pill on an empty stomach. They waited 30 minutes before food, drink, or other drugs. If they didn't follow those steps, less drug reached the blood. Your label and doctor can explain the timing.