Published in the New England Journal of Medicine in 2021, the STEP 1 trial randomized 1,961 adults with BMI of 30 or greater (or 27+ with a weight-related condition) to weekly semaglutide 2.4 mg or placebo for 68 weeks.

The semaglutide group achieved 14.9% mean weight loss compared to 2.4% with placebo. 86.4% of semaglutide participants achieved at least 5% weight loss, and 50.5% achieved 15% or greater loss. The most common adverse events were gastrointestinal (nausea, diarrhea, vomiting), but these led to treatment discontinuation in only 4.5% versus 0.8% on placebo.

Serious adverse events occurred at similar rates in both groups (9.8% semaglutide vs 6.4% placebo), with no individual serious adverse event occurring significantly more often with semaglutide. The trial demonstrated both substantial efficacy and acceptable tolerability over more than a year of treatment.

Published in Nature Medicine in 2022, the STEP 5 trial was designed specifically to assess whether semaglutide''s weight loss effects are maintained over 2 full years of treatment. It randomized 304 adults to semaglutide 2.4 mg or placebo for 104 weeks.

Mean weight loss was 15.2% with semaglutide versus 2.6% with placebo at week 104. 77.1% of the semaglutide group achieved at least 5% weight loss and maintained it for the full 2-year period. The trial completion rate of 92.8% was remarkably high, indicating that the treatment was well-tolerated over extended use.

The sustained efficacy over 2 years addresses a key concern about weight loss interventions: whether they work only short-term. STEP 5 demonstrated that weight loss is not only achieved but maintained with continued treatment, with no evidence of diminishing effectiveness or accumulating safety signals over the longer timeframe.

Published in the New England Journal of Medicine in 2023, the SELECT trial was the largest and longest cardiovascular outcome trial for any weight loss medication. It enrolled 17,604 adults with established cardiovascular disease and BMI of 27 or greater (without diabetes) and followed them for a mean of 39.8 months.

Semaglutide reduced major adverse cardiovascular events (MACE, defined as cardiovascular death, nonfatal heart attack, or nonfatal stroke) by 20% compared to placebo (hazard ratio 0.80, 95% CI 0.72-0.90, P<0.001). MACE occurred in 6.5% of the semaglutide group versus 8.0% of the placebo group.

This trial was transformative because it demonstrated that semaglutide does not merely help people lose weight but actively prevents the cardiovascular events that are the leading cause of death in people with obesity. No previous weight loss drug had ever demonstrated cardiovascular protection in a dedicated outcomes trial of this scale.

The FDA approved Wegovy (semaglutide 2.4 mg weekly injection) on June 4, 2021 for chronic weight management in adults with BMI of 30 or greater, or BMI of 27 or greater with at least one weight-related comorbidity. The approval was based on the STEP clinical trial program.

On March 8, 2024, the FDA expanded Wegovy''s approved indications to include reducing the risk of cardiovascular death, heart attack, and stroke in adults with established cardiovascular disease who also have obesity or overweight. This made semaglutide the first weight loss medication ever approved specifically to prevent cardiovascular events.

FDA approval requires demonstration of both efficacy and an acceptable safety profile based on comprehensive clinical data review. The cardiovascular indication expansion was particularly notable because it was based on the SELECT trial''s 39.8-month mean follow-up, providing longer-term safety data than is typical at the time of initial drug approval.

Published in The Lancet in 2021, the STEP 2 trial specifically tested semaglutide 2.4 mg in adults who had both type 2 diabetes and overweight/obesity, a population with complex metabolic needs and higher cardiovascular risk.

The semaglutide group achieved 9.6% mean weight loss compared to 3.4% with placebo at 68 weeks. 68.8% of semaglutide participants achieved at least 5% weight loss. In addition to weight loss, HbA1c (a measure of blood sugar control over 3 months) improved by approximately 1.6 percentage points more than placebo.

The dual benefit of weight loss and improved glycemic control in people with diabetes, without increased hypoglycemia risk, demonstrated that semaglutide is safe and effective even in a metabolically complex population. People with type 2 diabetes are at elevated risk for cardiovascular and kidney disease, making the safety profile in this group particularly important.

Published in JAMA in 2021, the STEP 3 trial tested whether semaglutide combined with intensive behavioral therapy (including a low-calorie diet for the first 8 weeks and regular counseling sessions) could produce greater weight loss. 611 participants were randomized.

The semaglutide plus behavioral therapy group lost 16% of body weight (approximately 37 lbs) versus 5.7% (14 lbs) with placebo plus behavioral therapy at 68 weeks. 75% of the semaglutide group achieved 10% or greater weight loss compared to 27% on placebo. The combination approach produced the largest weight losses seen in the STEP program.

The tolerability was consistent with other STEP trials, with gastrointestinal events as the most common side effects. The finding that even with intensive behavioral support, the placebo group only achieved 5.7% loss while the semaglutide group achieved 16% demonstrates that the pharmacological intervention adds substantial benefit beyond what lifestyle changes alone can achieve.

Published in JAMA in 2021, the STEP 4 trial used a novel design: all 803 participants received semaglutide for 20 weeks (run-in period), then were randomized to continue semaglutide or switch to placebo for an additional 48 weeks.

Those who continued semaglutide achieved 17.4% total weight loss by week 68, while those switched to placebo regained weight. The continued-treatment group maintained and extended their weight loss, demonstrating that the drug''s benefits persist with ongoing use without accumulating safety problems.

The trial''s design was specifically chosen to demonstrate the maintenance of benefit, showing that semaglutide works as a chronic treatment (similar to blood pressure or cholesterol medications) rather than a short-term intervention. The safety profile remained consistent during the full 68 weeks of treatment with no new safety signals emerging in the extended period.

In July 2023, the European Medicines Agency (EMA) launched a safety review after receiving approximately 150 reports of suicidal thoughts and self-harm in patients taking GLP-1 receptor agonists including semaglutide. The Pharmacovigilance Risk Assessment Committee (PRAC) conducted a thorough investigation.

In April 2024, PRAC concluded that the available evidence does not support a causal link between GLP-1 receptor agonists and suicidal or self-injurious thoughts. No product information update was warranted. The committee noted that the reporting rate was consistent with background rates of suicidal ideation in the obese and diabetic populations that use these drugs.

A separate study published in Nature Medicine in 2024 analyzed real-world claims data and found that semaglutide was actually associated with lower risk of suicidal ideation compared to other anti-obesity medications, providing additional reassurance beyond the regulatory investigation.

Published in 2024, real-world effectiveness studies of semaglutide for weight management confirmed that the weight loss observed in controlled clinical trials translates to routine clinical practice. In remote weight management programs, 83.1% of patients achieved 10% or greater weight loss and 56.2% achieved 15% or greater at 12 months.

Sustained weight loss was observed at 18-24 month follow-up in real-world practice settings. The consistency between clinical trial results and real-world outcomes is notable because real-world patients often have more comorbidities, less adherence support, and more concomitant medications than trial participants.

Real-world safety data also confirmed the clinical trial findings, with gastrointestinal side effects as the most common complaint but serious adverse events remaining rare. The convergence of controlled trial and real-world evidence strengthens confidence that semaglutide is both effective and safe when used as directed in typical clinical practice.

Across the STEP 1 through STEP 5 clinical trials, over 4,500 participants received semaglutide 2.4 mg for periods ranging from 68 to 104 weeks. The aggregate safety data from this program formed the basis of FDA and EMA regulatory approvals.

No deaths in any STEP trial were attributed to semaglutide. Serious adverse events occurred at rates similar between semaglutide and placebo groups. Treatment discontinuation due to adverse events was consistently below 7% across all trials, indicating that the vast majority of patients tolerate the medication well enough to continue treatment.

The longer-duration STEP 5 trial (104 weeks) and the SELECT cardiovascular trial (mean 39.8 months) did not reveal safety signals that were absent in the shorter trials, providing reassurance that extended treatment does not unmask delayed toxicity. This cumulative evidence base across thousands of patients and multiple years of exposure is substantially larger than what existed for most previously approved weight loss medications at the time of their approval.