Semaglutide and tirzepatide are the two medications almost every online weight-loss provider is actually selling, whatever the branding on the website says. They are not the same drug, they do not work in quite the same way, and the difference between them is the single most consequential choice you will make in this category - more consequential than which telehealth company you buy from.
The short answer
Tirzepatide produced more weight loss in its trials. Semaglutide has the longer track record, a wider set of approved uses, more supply routes and - at the moment - lower prices. If maximum weight loss is the priority and cost is not the binding constraint, tirzepatide is the stronger option. If you want the cheapest legitimate route to an FDA-approved GLP-1, semaglutide is currently it.
How they actually differ
Semaglutide is a GLP-1 receptor agonist. It mimics glucagon-like peptide-1, a hormone your gut releases after eating, which slows gastric emptying, signals fullness to the brain and dampens appetite. It is sold as Wegovy for weight management, Ozempic for type 2 diabetes, and Rybelsus as an oral tablet for diabetes. A once-daily oral form approved for chronic weight management is now on the market too.
Tirzepatide is a dual agonist: it activates both the GLP-1 receptor and the GIP receptor (glucose-dependent insulinotropic polypeptide). GIP is a second gut hormone involved in insulin response and fat metabolism. Hitting two pathways rather than one is the accepted explanation for why tirzepatide outperformed semaglutide on weight in trials. It is sold as Zepbound for weight management and Mounjaro for type 2 diabetes.
| Semaglutide | Tirzepatide | |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | Dual GIP and GLP-1 receptor agonist |
| Weight-loss brand | Wegovy (injection), oral Wegovy (tablet) | Zepbound |
| Diabetes brand | Ozempic, Rybelsus | Mounjaro |
| Average weight loss in trials | ~15% over 68 weeks (STEP 1) | ~20% over 72 weeks (SURMOUNT-1) |
| Dosing | Once weekly injection, or once daily tablet | Once weekly injection |
| Dose range | 0.25 mg up to 2.4 mg | 2.5 mg up to 15 mg |
| Typical self-pay cost | From roughly $149/month | Typically $199-$499/month |
What the trials actually showed
In STEP 1, adults with obesity and without diabetes taking semaglutide 2.4 mg alongside lifestyle intervention lost an average of about 15% of body weight over 68 weeks, against roughly 2.4% on placebo. In SURMOUNT-1, adults taking tirzepatide at the highest dose lost an average of about 20% of body weight over 72 weeks, against roughly 3% on placebo.
Two caveats matter more than most people realise. First, these are averages: a meaningful minority of participants lost far more, and a meaningful minority lost very little. Second, these are different trials with different populations and durations. The comparison is indicative, not a head-to-head result at every dose.
A number worth knowing
Side effects
The side-effect profiles are close cousins. Both commonly cause nausea, vomiting, diarrhoea, constipation and abdominal pain, and both are hardest during dose escalation. Both carry the same boxed warning about thyroid C-cell tumours and are contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or MEN 2. Both carry warnings for pancreatitis, gallbladder disease, kidney injury from dehydration and aspiration risk under anaesthesia.
There is no reliable way to predict which you will tolerate better. People who cannot get past the nausea on one sometimes do fine on the other, which is a legitimate reason to switch - and a reason to prefer a provider that lets you. Our side-effect guide covers management in detail.
Cost
Semaglutide currently wins on price, largely because Novo Nordisk began selling brand-name Wegovy direct to consumers. That has compressed the gap between brand-name and compounded semaglutide to almost nothing in some cases.
Tirzepatide costs more, and it has a structural problem semaglutide does not: it titrates across six dose levels from 2.5 mg to 15 mg, and providers that price per milligram will raise your bill every time you step up. Over a year that difference is larger than the difference between most providers' headline prices. A handful of providers hold the rate flat at any dose, and that is worth more than a cheap first month. See the full cost guide.
Which should you choose
Tirzepatide is usually the better fit if
- •You have a large amount of weight to lose and want the strongest option available
- •You have tried semaglutide and plateaued or did not respond
- •You can absorb a higher monthly cost, or you have insurance coverage for Zepbound
Semaglutide is usually the better fit if
- •Cost is the binding constraint - it is the cheapest FDA-approved route right now
- •You want the longest real-world safety record of the two
- •You would rather take a daily tablet than a weekly injection, which only semaglutide offers among these two
- •You have type 2 diabetes and want a medication with a longer history in that indication
Whichever way you lean, the decision belongs to a prescriber who knows your medical history. Both drugs have contraindications that rule some people out entirely, and neither is appropriate simply because you would like to weigh less. Check the eligibility criteria before you start comparing providers.
Where to get them
Both are available through dozens of online providers, in brand-name and compounded form. We rank them separately because the market for each looks quite different:
- •Best semaglutide providers - including the manufacturer's own direct pharmacy
- •Best tirzepatide providers - with the flat-rate plans flagged
- •Wegovy vs Zepbound - the two brand-name products compared directly