The GLP-1 receptor agonist behind Ozempic and Wegovy — how it works, how to titrate safely, and what to expect from weekly dosing.
Semaglutide is a GLP-1 receptor agonist — a synthetic analog of glucagon-like peptide-1 (GLP-1), a hormone your gut releases after eating. Natural GLP-1 breaks down within minutes; semaglutide is modified to last around a week, allowing once-weekly dosing.
It is FDA approved as Ozempic (subcutaneous, T2DM), Wegovy (subcutaneous, chronic weight management), and Rybelsus (oral, T2DM and — at 25 mg — chronic weight management since 2025). The Phase 3 obesity program (STEP) showed an average ~15% body-weight reduction at 68 weeks on 2.4 mg weekly (Wilding 2021 NEJM, PMID 33567185). The T2DM program (SUSTAIN) used lower max doses (1.0–2.0 mg) and produced smaller weight loss in diabetic populations.
FDA approved. Prescription-only in the US. The FDA-declared semaglutide shortage was resolved February 21, 2025; the 503A compounding enforcement deadline passed April 22, 2025 and the 503B deadline May 22, 2025, so broad compounded-semaglutide availability has ended. Research-grade unapproved-source material is sold by some suppliers as RUO; FDA has issued multiple warnings about salt forms (semaglutide sodium / acetate), which are not the same active ingredient as the approved base. Not WADA prohibited.
Acts on GLP-1 receptors in the hypothalamus to reduce hunger and increase the feeling of fullness. Most users report significantly reduced “food noise.”
Slows how fast food leaves the stomach, extending fullness per meal. This is also why nausea is the most common early side effect.
Enhances glucose-dependent insulin secretion and suppresses glucagon — lowers HbA1c without causing hypoglycemia in non-diabetics.
SELECT (Lincoff 2023 NEJM, PMID 37952131) showed a 20% reduction in major cardiovascular events (HR 0.80, 6.5% vs 8.0%) in overweight/obese patients with existing cardiovascular disease — independent of diabetes status.
Semaglutide is one of the most rigorously studied weight-management drugs ever approved — with decades of GLP-1 biology and multiple Phase 3 programs.
| Benefit | Evidence |
|---|---|
| Weight loss | STEP 1 (Wilding 2021 NEJM, PMID 33567185): ~14.9% body-weight loss vs 2.4% placebo at 68 weeks on 2.4 mg weekly |
| HbA1c reduction | SUSTAIN program (Aroda 2019 pooled, PMID 30615985): HbA1c reduction ~1.0–1.8% depending on dose (0.5 vs 1.0 mg) and comparator in T2DM |
| Cardiovascular events | SELECT in obesity without diabetes (PMID 37952131): HR 0.80 for MACE. Original T2DM CV signal: SUSTAIN-6 (Marso 2016 NEJM, PMID 27633186): HR 0.74 |
| Kidney protection | FLOW (Perkovic 2024 NEJM, PMID 38785209): HR 0.76 for kidney composite (kidney failure, ≥50% eGFR drop, kidney/CV death) in T2DM with CKD |
| Addiction / craving | Emerging evidence of reduced alcohol and nicotine cravings via mesolimbic dopamine pathway (observational + small mechanistic trials; no Phase 3 RCT yet) |
| MASH (liver) | ESSENCE Part 1 (Sanyal 2025 NEJM, PMID 40305708): semaglutide 2.4 mg over 72 weeks resolved MASH without worsening fibrosis and improved fibrosis without worsening MASH; FDA review pending for a MASH indication |
Build your protocol, log every dose, monitor your body's response, and get reminders so you never miss a dose.
Start Tracking FreeSlow titration is critical. Jumping doses is the #1 cause of severe GI side effects.
| Weeks | Weekly Dose |
|---|---|
| 1–4 | 0.25 mg |
| 5–8 | 0.50 mg |
| 9–12 | 1.0 mg |
| 13–16 | 1.7 mg |
| 17+ | 2.4 mg (max) |
If side effects at any step, hold for an extra 4 weeks before advancing. Some users find adequate response at 1.0–1.7 mg and individualize to a sub-maximum maintenance dose. The FDA label maintenance dose is 2.4 mg (or 1.7 mg if 2.4 isn’t tolerated); sub-label maintenance is consistent with ADA 2026 individualization guidance but is empirical, not label-endorsed.
Post-goal management is not yet RCT-validated. STEP 4 (PMID 33755728) showed participants who switched to placebo after a 20-week run-in regained ~7 percentage points of body weight over the following 48 weeks, while those continuing semaglutide lost an additional ~8% — full discontinuation drives substantial regain. Some clinicians taper to 0.5–1.0 mg weekly maintenance as empirical practice (not labeled or guideline-endorsed). Plan for long-term dosing rather than a short course.
FDA resolved the semaglutide shortage on February 21, 2025; 503A and 503B compounding enforcement deadlines passed April–May 2025. The reconstitution workflow below applies to research-supply / RUO material; per FDA, “Patients should not use compounded drugs if an approved drug is available.”
Semaglutide from research suppliers typically comes as a 5 mg or 10 mg lyophilized vial. Branded Ozempic/Wegovy pens come pre-filled and do not need reconstitution.
5 mg vial + 2 mL BAC water = 2.5 mg/mL = 2500 mcg/mL
| Dose | Volume | Syringe Units |
|---|---|---|
| 0.25 mg | 0.10 mL | 10 units |
| 0.50 mg | 0.20 mL | 20 units |
| 1.0 mg | 0.40 mL | 40 units |
| 1.7 mg | 0.68 mL | 68 units |
| 2.4 mg | 0.96 mL | 96 units |
5 mg vial at 0.5 mg/week = 10 weeks; at 2.4 mg/week = ~2 weeks
Pre-filled with a typical Semaglutide setup. Edit any field — the draw updates live.
Insulin syringe — 100 units = 1 mL
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FDA boxed warning for thyroid C-cell tumors (based on rodent data; human relevance uncertain but strictly avoid with MTC/MEN2 history).
How much protein do I need while on semaglutide?
Target at least 1 g protein per pound of lean body mass and strength train 2–3×/week to preserve muscle during weight loss.
What if nausea is severe?
Eat smaller meals, avoid high-fat meals, stay hydrated. If persistent or severe vomiting occurs, hold the dose and work with a doctor — this is not normal.
Do I need labs?
Baseline CBC, CMP (including liver and kidney), lipase/amylase, thyroid panel, HbA1c. Recheck every 3–6 months. Monitor heart rate (can increase with GLP-1s).
Semaglutide vs. tirzepatide?
Tirzepatide (Mounjaro / Zepbound) is a dual GLP-1/GIP agonist — more weight loss on average. The 2025 SURMOUNT-5 head-to-head (PMID 40353578) showed ~20% weight loss on tirzepatide vs. ~14% on semaglutide at 72 weeks in obesity without T2D. Side-effect profiles are broadly similar; semaglutide has more long-term safety data.
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Build your protocol, log every dose, monitor your body's response, and get reminders so you never miss a dose.
Start Tracking FreeYes. Semaglutide is FDA approved under three brand names: Ozempic (subcutaneous, type 2 diabetes, approved Dec 2017), Wegovy (subcutaneous, chronic weight management in adults with obesity or overweight + comorbidity, approved June 2021), and Rybelsus (oral, type 2 diabetes and obesity). Research-grade semaglutide sold by peptide vendors is NOT an FDA-approved drug — it is sold only as a research chemical.
The FDA label for Wegovy (weight management) titrates monthly: 0.25 mg/week for 4 weeks, 0.5 mg/week for 4 weeks, 1.0 mg/week for 4 weeks, 1.7 mg/week for 4 weeks, then 2.4 mg/week as the maintenance dose. Ozempic (T2DM) tops out at 2.0 mg/week. Slower titration is sometimes used to reduce GI side effects.
For a 5 mg lyophilized vial, a typical reconstitution is 5 mg + 2 mL of bacteriostatic water, yielding a concentration of 2.5 mg/mL. A 0.25 mg starting dose draws to 0.10 mL (10 units on a 50-unit insulin syringe). At maintenance (2.4 mg), the draw becomes 0.96 mL — close to a full 1 mL insulin syringe.
Appetite suppression is often noticeable within the first 1–2 weeks. Meaningful weight loss begins around weeks 4–8 as the dose titrates upward. In the STEP-1 trial, average weight loss reached approximately 15% of body weight at 68 weeks on the 2.4 mg maintenance dose.
Per the FDA label, the most common adverse reactions (≥5% of patients) are gastrointestinal: nausea, diarrhea, vomiting, constipation, abdominal pain, headache, fatigue, dyspepsia, dizziness, abdominal distension, eructation, hypoglycemia (in T2DM), flatulence, gastroenteritis, and GERD. Most GI events are dose-dependent and tend to attenuate with continued treatment. The label carries a boxed warning for thyroid C-cell tumors based on rodent studies.
Semaglutide is a single GLP-1 receptor agonist. Tirzepatide is a dual agonist of both GLP-1 and GIP receptors. In the head-to-head SURMOUNT-5 trial, tirzepatide produced greater weight loss than semaglutide at 72 weeks (~20% vs. ~14%). Both are FDA approved for chronic weight management; tirzepatide currently produces the largest weight-loss results of any approved medication.
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