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; 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.
Worth stating plainly, because it is the most common misunderstanding about this class: semaglutide does not burn fat. There is no mechanism here that oxidises fatty acids or raises metabolic rate. Every mechanism above acts on intake — appetite, satiety, food reward, gastric emptying.
All of the weight loss therefore comes from one thing: it becomes much easier to eat less than you burn. The calorie deficit is what reduces fat mass. The drug's contribution is making that deficit sustainable rather than a daily fight against hunger.
This is not a technicality — it explains the withdrawal data directly. When the drug stops, the appetite suppression stops, and the deficit stops with it unless something else is holding it in place. That is why the STEP 1 extension found most of the lost weight returned within a year, and it is why the same trials pair the drug with lifestyle intervention rather than testing it alone.
Build your protocol, log every dose, monitor your body's response, and get reminders so you never miss a dose.
Start Tracking FreeSemaglutide 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 |
Weight loss and fat loss are not the same measurement, and this is the question most often asked by people who train. Scale weight includes fat, lean tissue, and water; a drug that reduces appetite reduces intake of everything, not selectively of fat.
The most informative recent data comes from the SEMALEAN study (Alissou et al., 2026, PMID 41068996), a prospective study of patients with obesity on semaglutide 2.4 mg, with body composition measured by DXA rather than estimated. Of 115 enrolled, 106 completed, at a mean BMI of 46.3.
That is a more encouraging picture than the common forum framing of steady muscle wasting, and the strength finding in particular is worth sitting with: function and mass are separate things, and they moved in opposite directions here.
Read it with its limits in view, though. SEMALEAN is a single-arm prospective study, not a randomised controlled trial. There is no control group, so it cannot separate the drug's contribution from everything else changing over twelve months. It also studied one cohort at a high starting BMI, which may not generalise. It is good evidence of what happened to these patients; it is not proof of what the drug does to lean mass in general.
The literature consistently identifies resistance training and protein intake as the factors that modify this ratio. How much of either is appropriate for a given person is a question for a clinician or dietitian who knows their situation — not something to take from a guide.
Pre-filled with a typical Semaglutide setup. Edit any field — the draw updates live.
Insulin syringe — 100 units = 1 mL
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Not medical advice. These figures describe what is reported in the literature and what practitioners and communities do — not a recommendation, and for most compounds here no human dose-finding study exists. Talk to a qualified healthcare provider.
The protocol below is the studied protocol. Semaglutide is an approved medicine, and the titration to 2.4 mg weekly is what the STEP trials used and what the label specifies — not a community extrapolation. The diabetes range (0.5–2.0 mg) and the 25 mg oral dose are likewise approved dosing. That puts this compound in a small minority on this site.
Slow 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.
Not medical advice. These figures describe what is reported in the literature and what practitioners and communities do — not a recommendation, and for most compounds here no human dose-finding study exists. Talk to a qualified healthcare provider.
FDA resolved the semaglutide shortage on February 21, 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
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.
Reported often enough to be worth naming. A 2026 systematic review and meta-analysis of GLP-1 receptor agonists (Viquez Burboa et al., PMID 42621629) pooled 17 studies covering 1,091,743 patient-exposures and found a pooled odds ratio of 1.40 (95% CI 1.33–1.48) for non-scarring alopecia, with no heterogeneity between the cohort studies. The subtypes involved are telogen effluvium and androgenetic alopecia.
The proposed mechanism is not a direct drug effect on hair follicles but the physiological stress and micronutrient shortfall that accompany rapid weight loss — telogen effluvium is a well-known consequence of rapid weight loss by any method, including surgery and dieting. That reframes it: the shedding tracks how fast weight is coming off, not the molecule as such.
Semaglutide is sold for research use only. StackTrax does not sell it, does not endorse personal use, and does not point to a specific supplier for it.
Quality varies enormously among research-chemical suppliers. At minimum, look for:
Lyvn is the vendor we recommend elsewhere on this site — every batch third-party tested, with the full independent panel published per batch. We are not making a recommendation for Semaglutidespecifically; their catalogue is simply a worked example of the criteria above.
For research use only. Not for human consumption. 21+.
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.
Disclaimer: This guide is for educational and informational purposes only and is not intended as medical advice, diagnosis, or treatment. The compounds discussed are not FDA approved for human use. Always consult a qualified healthcare provider before starting any new supplement or peptide protocol. StackTrax does not sell peptides or supplements directly — purchase links go to third-party vendors. StackTrax is not responsible for the products, quality, or business practices of any third-party vendor.
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StackTrax guides cover peptides and compounds that are not FDA-approved for the uses discussed. The dosing, reconstitution, and safety information is compiled from published research and community protocols for educational purposes only.
Before using any compound mentioned here, consult a qualified healthcare provider. StackTrax does not sell, prescribe, or recommend these substances for personal use.