In plain English
Semaglutide copies a natural gut hormone called GLP-1 that tells your brain you are full and helps your body manage blood sugar. Injected once a week, it lowers appetite, so people eat less and lose weight. It is one of the most studied weight-loss peptides in the world.
What it's used for
- Weight management in adults and teens 12+ (Wegovy)
- Type 2 diabetes: lowering blood sugar (Ozempic)
- Lowering the risk of heart attack and stroke in adults with heart disease and excess weight (Wegovy)
- Also being studied for fatty liver disease, kidney disease and sleep apnea
Benefits
In human studies, semaglutide has shown:
- About 15% average weight loss over 68 weeks at 2.4 mg weekly (STEP 1)
- About 21% average weight loss over 72 weeks at 7.2 mg weekly (STEP UP)
- A 20% lower risk of heart attack, stroke or cardiovascular death (SELECT, about 17,600 adults)
- Large, consistent drops in blood sugar and HbA1c
- Less hunger and fewer food cravings
How it works
In simple terms: semaglutide turns up your body’s “I’m full” signal.
It binds to the GLP-1 receptor, the same receptor your own GLP-1 hormone uses after a meal. That slows stomach emptying, reduces hunger signals in the brain, helps the pancreas release insulin only when blood sugar is high, and lowers glucagon (a hormone that raises blood sugar). Natural GLP-1 lasts only a couple of minutes in the blood. Semaglutide was engineered with a fatty-acid side chain that binds to albumin in the blood, which stretches its half-life to about a week and allows once-weekly dosing.
Development history
Semaglutide was developed by Novo Nordisk as a longer-lasting successor to liraglutide.
- 2017: Ozempic is FDA-approved for type 2 diabetes.
- 2021: Wegovy (2.4 mg weekly) is FDA-approved for weight management.
- 2024: Wegovy is approved to lower cardiovascular risk.
- 2026: Wegovy HD (7.2 mg weekly) is approved for adults with obesity.
Typical protocols
Branded semaglutide comes in pre-filled pens. These schedules follow the prescribing label.
| Product | Starting dose | Step-up | Maintenance |
|---|---|---|---|
| Wegovy (weekly) | 0.25 mg for 4 weeks | 0.5 → 1 → 1.7 mg, each for 4 weeks | 2.4 mg weekly (or 1.7 mg) |
| Wegovy HD (weekly) | Stepped up beyond 2.4 mg | 7.2 mg weekly | |
| Ozempic (weekly) | 0.25 mg for 4 weeks | 0.5 mg, then 1 mg and 2 mg if needed, at least 4 weeks at each dose | 0.5–2 mg weekly |
Semaglutide is also available as powder in vials that are mixed with bacteriostatic water. Users report following the same start-low, step-up pattern as the pens, using the calculator below to turn each mg dose into syringe units.
Cycling
Semaglutide is used continuously rather than cycled. When people stop, appetite tends to return and much of the lost weight can come back over the following year. After a break of more than about two weeks, people usually restart at a lower dose to limit stomach side effects.
Administration options
Subcutaneous injection once a week, on the same day each week, in the belly, thigh or upper arm. Time of day and meals do not matter.
Reconstitution and dosing calculator
Pens need no mixing. The calculator below is for semaglutide powder in vials, which is commonly mixed with 2 mL of bacteriostatic water.
Draw your syringe to
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- Each unit holds
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- Doses per vial
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Show the math
This tool does arithmetic only. It does not choose a dose or confirm that any substance is right for you. Double-check every result against your syringe and your clinician’s instructions.
Side effects and safety
- Most common: nausea, diarrhea, vomiting, constipation, stomach pain, headache, tiredness and heartburn. These are usually worst when starting or raising the dose and ease over time.
- The prescribing label warns about thyroid C-cell tumors seen in rodents. People with a personal or family history of medullary thyroid cancer or MEN 2 syndrome should not use it.
- Other risks listed on the label: pancreatitis, gallbladder problems, low blood sugar when combined with insulin or sulfonylureas, kidney strain from dehydration, allergic reactions and worsening diabetic eye disease.
- Not for use during pregnancy; the label advises stopping at least 2 months before a planned pregnancy.
- Fast weight loss can include some muscle loss; enough protein and strength training help.
Common stacks
- Cagrilintide: an amylin analog paired with semaglutide in the combination CagriSema.
- Not combined with tirzepatide, retatrutide or other GLP-1 peptides, since they work on the same receptor.
- Users report pairing it with BPC-157 for stomach comfort.
Storage
Unopened pens: refrigerate at 2–8 °C (36–46 °F). Do not freeze.
Pens in use: follow the label’s room-temperature allowance.
Vials: keep powder cold and dry; after mixing, refrigerate and protect from light.
Compare with
- Tirzepatide: acts on GLP-1 and GIP receptors and produced more weight loss than semaglutide in head-to-head studies.
- Retatrutide: a newer triple agonist (GLP-1, GIP and glucagon) with even larger weight loss in studies.
- Liraglutide: an older, daily GLP-1 with smaller average weight loss.
Frequently asked questions
Is Ozempic the same as Wegovy?
Both contain semaglutide. Ozempic is used for type 2 diabetes at doses up to 2 mg weekly; Wegovy is used for weight management at 2.4 mg (7.2 mg as Wegovy HD).
How long does it take to work?
Appetite often drops within the first few weeks. Because the dose is raised slowly, most weight loss happens over the first 12–18 months.
What happens if I stop?
Many people regain a large share of the lost weight within a year of stopping.
Is semaglutide from a vial the same as the pens?
It is the same molecule, but strength and purity depend on the supplier. A batch-specific third-party test (COA) is the best way to confirm what is in a vial.
References
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384:989-1002.
- Lincoff AM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). N Engl J Med. 2023;389:2221-2232.
- Wegovy (semaglutide) injection and Ozempic (semaglutide) injection, US prescribing information, Novo Nordisk.
- HCPLive. Higher-dose semaglutide (Wegovy HD) 7.2 mg for obesity. https://hcplive.com/view/fda-approves-higher-dose-semaglutide-wegovy-hd-injection-7-2-mg-for-obesity