The widely studied GLP-1 agonist behind modern weight-loss medicine — strong appetite control and metabolic benefits.
Semaglutide is a once-weekly GLP-1 receptor agonist — the single most studied compound in modern weight-loss medicine. It mimics the gut hormone GLP-1 to reduce appetite, increase fullness, slow gastric emptying, and improve insulin secretion.
Across the STEP trials it produced mean weight loss near 15% over 68 weeks, and the SELECT trial showed it reduces major cardiovascular events in people with overweight/obesity and established heart disease — a landmark result that moved GLP-1 drugs beyond weight and glucose alone.
It has the deepest safety and outcomes evidence of any peptide on this list. The trade-off versus tirzepatide and retatrutide is slightly less weight loss on average; the side-effect pattern is the familiar dose-dependent GI one, managed with monthly titration.
Reliable, well-evidenced appetite suppression and fat loss.
STEP trials: ~15% mean weight loss at 68 weeks
Lowers the rate of heart attack, stroke, and cardiovascular death in at-risk people — independent of diabetes.
SELECT trial: 20% reduction in major cardiac events
Strong, durable HbA1c reduction; one of the first-line injectable options.
SUSTAIN program: robust glycemic control
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Evidence Profile
The most thoroughly studied weight-loss peptide — large phase 3 trials plus cardiovascular-outcome evidence.
Backed by human clinical data — one or more controlled human trials show a consistent effect.
Controlled trials & clinical data in people
STEP, SUSTAIN, and SELECT trials; FDA-approved with cardiovascular-benefit data.
Preclinical results in animal models
Deep preclinical GLP-1 literature.
How plausibly it works at a biological level
GLP-1 receptor agonism is among the best-understood metabolic mechanisms.
Depth of documented safety in humans
Largest safety and outcomes dataset of any compound here; GI effects are the main tolerability issue.
Men who want the most evidence-backed option, especially with cardiovascular risk factors
Begin at 0.25 mg/week and step up monthly. Keep protein intake high and train to preserve lean mass. Separate from time-sensitive oral meds since it slows gastric emptying.
Women seeking sustained appetite control with the strongest safety track record
Discontinue at least 2 months before a planned pregnancy; not for use while pregnant or breastfeeding. Nausea is most common in the first weeks and eases with slow titration.
Extensively used by women. Discontinue at least 2 months before a planned pregnancy. Not for use while pregnant or breastfeeding.
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Contraindicated with personal or family history of medullary thyroid carcinoma or MEN 2.
Stop for signs of pancreatitis.
Begin at 0.25 mg/week and titrate monthly to limit nausea.
Can slow gastric emptying — separate from other oral medications.
Support muscle retention with protein and resistance training.
The effects most commonly reported with Semaglutide, when they tend to show up, and how to manage them.
Eat smaller, lower-fat meals; titrate slowly; it usually fades within 1–2 weeks at a stable dose.
Hydrate well, add fiber, stay active. Tell your clinician if severe or persistent.
Prioritize protein and don't under-eat — rapid loss can cost muscle. Lift weights.
Rotate sites; let alcohol dry fully before injecting.
Stop immediately and seek medical care — this is a red-flag symptom.
Individual responses vary. Stop and consult a clinician for severe, persistent, or unexpected reactions.
14 steps with photos, pro tips, and a dosing calculator.
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View Full GuidePepCompass provides educational information only. Nothing on this platform constitutes medical advice, diagnosis, or treatment. All content is for informational and research purposes only. Always consult a licensed healthcare provider before starting any peptide protocol. Individual results vary.