Semaglutide: What It Is, How It Works, and What It Costs

The Short Answer

Semaglutide is a once-weekly injectable medication, now also available as a tablet, that reduces appetite by mimicking a gut hormone. In its main obesity trial, adults taking it lost 14.9% of their body weight over 68 weeks, against 2.4% on placebo. Buying it direct from Novo Nordisk costs $349 a month for standard Wegovy doses. It is the most studied medication in its class.

What is semaglutide?

Semaglutide is a GLP-1 receptor agonist — a lab-made version of glucagon-like peptide-1, a hormone your gut releases after you eat.

Natural GLP-1 lasts minutes. Semaglutide is engineered to last days, which is why the injection is weekly rather than daily. It is a peptide, which is why it has historically had to be injected: peptides are broken down in the stomach. The oral tablet works around that with an absorption enhancer, which is why it carries food and water timing rules the injection does not.

Which brands contain semaglutide?

The distinction that trips people up: Ozempic and Wegovy contain the same drug. They differ in approved use and maximum dose. That is why a prescriber treating obesity should be writing for Wegovy rather than Ozempic, and why "Ozempic for weight loss" is an off-label conversation rather than a straightforward one. Ozempic's approved doses also top out lower than Wegovy's.

How does it work in the body?

Three effects drive the weight loss, and only one of them is the one most people expect.

It quiets appetite signalling in the brain. GLP-1 receptors sit in the appetite centres of the hypothalamus. Activating them reduces hunger and, in the phrase most patients reach for unprompted, turns down the "food noise."

It slows gastric emptying. Food leaves the stomach more slowly, so fullness arrives sooner on a smaller portion and lasts longer.

It improves blood sugar control. Semaglutide prompts insulin release only when glucose is elevated, which is why the class was developed for type 2 diabetes before anyone was studying it for weight.

What it does not do is burn fat, raise metabolism, or block absorption. The mechanism is appetite, which is also why appetite returns when the medication stops.

What does the evidence actually show?

The headline trial. STEP 1 followed 1,961 adults with obesity, or overweight with a weight-related condition, for 68 weeks. Mean weight loss was 14.9% on semaglutide 2.4 mg against 2.4% on placebo, from a mean starting weight of 105.3 kg. 86.4% of participants on semaglutide lost at least 5% of their body weight, against 31.5% on placebo.

Head to head against tirzepatide, it comes second. In SURMOUNT-5, a 72-week trial of 751 participants comparing the two directly, semaglutide produced 13.7% mean weight loss against tirzepatide's 20.2%. On the tougher thresholds the gap widens: 40.1% of the semaglutide group lost at least 15% of their body weight, against 64.6% on tirzepatide.

That is a real difference and it deserves to be stated plainly rather than buried. It is also not the whole decision — tolerance, cost, coverage and availability all vary by person. Our tirzepatide vs. semaglutide comparison works through the cases where the drug with the lower average is still the better choice for you.

On stopping. This is the finding clinics soft-pedal most often. In the STEP 1 extension, participants who came off semaglutide regained the majority of the weight they had lost within a year. These medications treat obesity rather than cure it, and any plan that assumes six months and done is a plan that has not read the data.

What are the side effects?

The common ones are gastrointestinal — nausea above all, then vomiting, constipation, diarrhoea and reflux. They cluster in the first weeks and after each dose increase, and they fade for most people as the body adjusts. Slow titration exists specifically to manage this. Some people find them intolerable and stop, which is a real outcome rather than a failure.

The serious ones are rare and worth knowing. Pancreatitis has been reported; severe, persistent abdominal pain is a call-your-doctor symptom rather than a wait-and-see one. Gallbladder problems occur at somewhat higher rates, partly a known consequence of rapid weight loss itself. Semaglutide carries a boxed warning for thyroid C-cell tumours based on rodent studies; it is not established that the risk applies to humans, but anyone with a personal or family history of medullary thyroid carcinoma or MEN 2 syndrome should not take it. It should not be used in pregnancy, and the Wegovy label advises stopping at least two months before a planned pregnancy.

Full detail, including the non-GLP-1 alternatives, is in Weight Loss Medications Explained. Ask your prescriber to walk the full list before you start; one who glosses over it is telling you something.

Is compounded semaglutide still available?

Mostly not, and this is the part of the picture that changed most recently.

Compounded semaglutide was widely available because semaglutide was on the FDA's drug shortage list, which permits compounding pharmacies to make copies of a drug patients cannot otherwise get. The FDA declared that shortage resolved on February 21, 2025. State-licensed pharmacies had until April 22, 2025 to wind down and outsourcing facilities until May 22, 2025.

With semaglutide off the shortage list, a compounded version is treated as an "essentially a copy" of an available commercial drug, which restricts compounding to cases where a prescriber documents a meaningful clinical difference for an individual patient. On April 30, 2026 the FDA proposed excluding semaglutide from the 503B bulks list outright, finding there is "no clinical need for outsourcing facilities to compound these drugs from bulk substances."

Platforms still advertising it exist. In March 2026 the FDA sent warning letters to 30 telehealth companies over how they market compounded GLP-1s, objecting to "claims implying sameness with FDA-approved products" and to firms "obscuring product sourcing by advertising drug products branded with the telehealth firm's name." No companies were named. If a provider offers you compounded semaglutide, ask which pharmacy fills it and on what basis, and treat an unwillingness to answer as the answer.

What does semaglutide cost?

Novo Nordisk now sells direct to cash-paying patients at published prices:

With commercial insurance that covers obesity treatment, Novo's savings card can bring it to as little as $25 a month, capped at $100 a month of assistance. Eligible Medicare Part D beneficiaries can pay $50 a month through the CMS Medicare GLP-1 Bridge, which runs from July 1, 2026 to December 31, 2027.

Telehealth platforms bundle a clinician and coaching on top and run $99 to $548 a month across the providers we track — worth comparing against the direct price rather than assuming, because since December 2025 the gap has closed considerably. Full breakdown in the GLP-1 Price Guide, or get a personalised estimate with the cost calculator.

Where to go next

Compare them directly in tirzepatide vs. semaglutide, read the tirzepatide guide, or browse providers and clinics that prescribe semaglutide. If you are choosing between buying direct, telehealth and a local clinic, that comparison is here.

Sources

• Novo Nordisk — STEP 1 trial results — 1,961 adults, 68 weeks, 14.9% vs 2.4%, 86.4% reaching ≥5%.
• Eli Lilly — SURMOUNT-5 head-to-head results — May 11, 2025; 751 participants, 72 weeks, semaglutide 13.7% vs tirzepatide 20.2%.
• FDA — FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize — shortage resolution February 21, 2025 and wind-down deadlines.
• FDA — FDA Proposes to Exclude Semaglutide, Tirzepatide, and Liraglutide on 503B Bulks List — April 30, 2026.
• FDA — FDA warns 30 telehealth companies against illegal marketing of compounded GLP-1s — March 3, 2026.
• Novo Nordisk / NovoCare — Wegovy self-pay price guide (PDF)
• CMS — Medicare GLP-1 Bridge
• Side effect, boxed warning and pregnancy statements are drawn from the FDA prescribing information for Wegovy and Ozempic.

*Every dated claim above was verified against the source linked beside it on the date shown at the top of this guide. This is not medical advice — talk to a licensed clinician before starting or changing any treatment.*