Semaglutide
The original weight-loss wave, sold as Ozempic / Wegovy. A GLP-1 agonist.
Semaglutide: The original weight-loss wave, sold as Ozempic / Wegovy. A GLP-1 agonist. Semaglutide is the first wave of modern weight-loss drugs, sold as Ozempic and Wegovy.
Semaglutide is the first wave of modern weight-loss drugs, sold as Ozempic and Wegovy. Single-receptor version of Tirzepatide. Slightly less effective and slightly rougher side effects, but well-studied and widely available.
Approved as Ozempic (2017, type 2 diabetes), Rybelsus (2019, oral), and Wegovy (2021, obesity).
FDA-approved drug products containing this substance are available. Compounded versions are not FDA-approved.
Yes, extremely widely prescribed. Insurance coverage variable for weight-loss indication.
Wear a CGM the first 14 days.
Same as tirz. A two-week sensor (~$80, OTC, no prescription) tells you more about how YOUR body is responding to Semaglutide than any protocol guide can. Most users wear one and don't again. The first cycle is the one that matters.
Who it's for
- โBeginners to GLP-class peptides
- โUsers with insurance coverage on Wegovy / Ozempic
- โMetabolic-syndrome adults under provider guidance
What to expect
- Week 1
Appetite drops. Nausea variable.
- Week 4
First titration. 2-4lb down typically.
- Week 8
5-8lb cumulative for most.
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How it works (mechanism)
GLP-1 receptor agonist resistant to DPP-4 enzymatic breakdown. Binds GLP-1 receptors in the brain (satiety), gut (delayed gastric emptying), and pancreas (glucose-dependent insulin secretion). Weekly dosing achieves steady-state GLP-1 signaling.
Dosing protocol
Stacks well with
Stack essentials
Side effects
When NOT to use
- โ MTC / MEN-2 history
- โ Pancreatitis history
- โ Pregnancy / nursing
Bloodwork to monitor
- โข Lipid panel
- โข ALT/AST
- โข A1C
Common mistakes
- โข Titrating too fast
- โข Skipping protein and lifting
- โข Treating it as a forever drug with no plan
What it actually is
A weekly injection that imitates GLP-1, one of the gut hormones released after a meal. It is an approved medicine sold as Ozempic for type 2 diabetes and Wegovy for weight management, and it is the drug that started the current weight-loss wave. Oral semaglutide now exists in two distinct labelled products: Rybelsus for type 2 diabetes, and the Wegovy tablet at 25 mg once daily, approved in December 2025 for weight management and cardiovascular risk reduction. Which oral product someone is describing matters, because the indications and doses are not the same.
GLP-1 is released by the intestine when food arrives. It prompts insulin release, suppresses glucagon, slows stomach emptying and acts on appetite centres in the brain. Semaglutide is a modified version that resists the enzyme that normally destroys GLP-1 within minutes, so a single injection keeps that signal running for about a week. You feel full sooner, stay full longer, and think about food less.
Forms, and which is which
Manufacturer auto-injector with assured identity and sterility. Wegovy is the obesity-labelled version at higher doses; Ozempic is the diabetes label.
Verdict: The reference form.
Absorption is poor and depends on taking it fasted with a small sip of water and waiting 30 minutes before anything else, which is a real adherence burden.
Verdict: Legitimate, fussy regimen, diabetes dosing.
Approved December 2025. The OASIS 4 trial reported roughly 16.6% mean weight loss with adherence, broadly comparable to the 2.4 mg injection. Same fasted-dosing burden as Rybelsus.
Verdict: A genuine oral option for weight, and a different product from Rybelsus.
Widespread during the shortage. Some compounded product used semaglutide salt forms, which are not the same molecule as the approved base and were the subject of FDA warnings.
Verdict: Ask what salt form it is; if nobody can answer, that is the answer.
Buyer-reconstituted, sold as not for human consumption, no identity or sterility assurance.
Verdict: Every quality risk in one vial.
What it is claimed to do, graded
The STEP programme is large, randomised and placebo-controlled, with meta-analyses on top. STEP 1, in people without diabetes, reported a mean change of -14.9% at week 68 against -2.4% on placebo. STEP 2, in people with type 2 diabetes, reported -9.6% โ the effect is consistently smaller when diabetes is present, and quoting the higher number to someone with diabetes overstates what they should expect.
The original indication, supported by the SUSTAIN phase 3 series.
Demonstrated in dedicated cardiovascular outcome trials, which is a higher bar than a surrogate marker and unusual for anything in this catalog. The population matters: the evidence is in people who already have cardiovascular disease, not in everyone taking it for weight.
Genuinely interesting early signals and small trials, plus a lot of anecdote. Not established, and being marketed well ahead of the evidence.
As with the rest of the class, a meaningful fraction of loss is lean tissue. Protein and resistance training are what address this.
Grades describe how much human evidence exists for that specific claim, not whether it will work for you or whether it is safe.
Pros and cons
- โข The best-evidenced weight-loss drug class in history, with cardiovascular outcome data behind it
- โข Weekly dosing and a well-understood titration schedule
- โข Oral options exist for both the diabetes and the weight-management labels
- โข Insurance coverage is more common than for newer agents
- โข Nausea is common and is the usual reason people stop
- โข Weight regain after stopping is well documented
- โข Compounded supply has included salt forms that are not the approved molecule
- โข Lean mass loss is real
- โข Gallbladder problems increase with rapid weight loss
When to stop
- โข Severe persistent abdominal pain radiating to the back
- โข A new neck lump, hoarseness or difficulty swallowing
- โข Vomiting that prevents keeping fluids down
- โข Right upper abdominal pain with fever or jaundice
- โข A resting heart rate that climbs and stays up, or palpitations at rest
- โข New or worsening vision changes โ rapid glucose improvement can transiently worsen diabetic retinopathy
- โข Pregnancy. Labelling advises stopping at least two months before a planned pregnancy, because it clears slowly
Interactions
Additive glucose lowering, real hypoglycaemia risk. Dose adjustment of the other drug is a prescriber decision.
Slowed gastric emptying changes absorption rate, and the guidance is monitoring for narrow-therapeutic-index drugs rather than a timing workaround. The oral tablet is the exception: it must be taken at least 30 minutes before anything else.
Worsens nausea and compounds hypoglycaemia risk when intake is already low.
Retained stomach contents despite fasting has prompted specific pre-operative guidance. Tell the anaesthetist you are on it โ withholding a dose is not established to remove the risk.
Labelling does not recommend combining these. No added benefit, multiplied effects.
Oral semaglutide increased levothyroxine exposure by about a third. This is specific to the tablet, not the injection.
The countermeasure to lean mass loss.
Is this for you?
- โข Adults with obesity or type 2 diabetes working with a prescriber
- โข People who want the option with the longest safety record and cardiovascular outcome data
- โข Anyone whose insurance covers Wegovy or Ozempic
- โข Personal or family history of medullary thyroid carcinoma or MEN-2
- โข You have had a serious hypersensitivity reaction to semaglutide or any ingredient in it
- โข You have severe gastroparesis โ labelling does not recommend use
- โข You are pregnant. A prior episode of pancreatitis is not an automatic exclusion but does need a clinician's assessment rather than a decision made here
The one number
Sources for the claims above
- Mean body weight change of -14.9% at week 68 in adults without diabetes (STEP 1)
- Mean body weight change of -9.6% at week 68 in adults with type 2 diabetes (STEP 2)
- Systematic review and meta-analysis of weight loss in obesity without diabetes
- Safety profile review
Drug & supplement interactions
- โ Insulin and sulfonylureas: dose reduction usually needed to prevent hypoglycemia
- โ Slows gastric emptying, affects oral medication absorption (especially time-sensitive drugs like contraceptives)
- โ Warfarin: monitor INR more closely after starting
- โ Avoid alcohol during titration steps (worsens nausea)
The Pepdex take
Aggressive muscle loss is the most under-discussed side effect of running Semaglutide aggressively. Not technically a side effect, a feature of how rapid the weight loss is when you're not eating enough protein or lifting heavy. Plenty of users drop 30 lbs and somehow look worse in the mirror. Lift heavy 3x/week, hit 0.8-1g protein per lb of bodyweight, or expect skinny-fat results. If those aren't on the table, run Tirz at a lower dose instead.
Community patterns
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Common questions about Semaglutide
Tracked alongside Semaglutide
Same goal, different aisle โ each graded on its own evidence in the Pepdex catalog.
More in Fat Loss
Strong weight loss with a cleaner side effect profile than semaglutide. A dual agonist (GLP-1 + GIP), FDA-approved as Mounjaro / Zepbound.
Triple agonist (GLP-1 + GIP + glucagon) from Eli Lilly. In trials it outperforms Tirzepatide for weight loss.
Daily GLP-1 receptor agonist. FDA-approved 2010 (Victoza, T2D) and 2014 (Saxenda, obesity). The first wave of modern GLP-1 weight-loss therapy and direct predecessor to Semaglutide.
An appetite-control shot for weight loss. A long-acting amylin agonist that works on a different pathway than the GLP-1 drugs, often paired with Semaglutide as 'CagriSema' to break GLP-1 plateaus.