Semaglutide and tirzepatide are the two molecules behind almost every GLP-1 weight loss headline of the past three years. Semaglutide is sold as Wegovy for weight management and Ozempic for type 2 diabetes; tirzepatide is sold as Zepbound for weight management and Mounjaro for type 2 diabetes. They are not the same drug, they do not work identically, and the difference between them affects results, side effects, and cost. This guide sets out what the evidence actually shows and how to think about choosing.

Quick Takeaway:

• Semaglutide is a GLP-1 receptor agonist; tirzepatide activates both the GLP-1 and GIP receptors
• In pivotal trials, semaglutide 2.4 mg produced around 15% mean weight loss at 68 weeks; tirzepatide produced roughly 16.5% to 22.4% over 72 weeks depending on dose
• Tirzepatide has produced greater average weight loss, but individual response varies widely
• Gastrointestinal side effects are common with both and are the leading reason people stop
• Cost, tolerability, and availability often matter more in practice than the average trial difference

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How They Work

Semaglutide is a GLP-1 receptor agonist. It mimics glucagon-like peptide-1, an incretin hormone released after eating. Activating the GLP-1 receptor slows gastric emptying, increases satiety signalling in the brain, and improves glucose-dependent insulin secretion. The net effect is that you feel full sooner, stay full longer, and eat less without consciously restricting.

Tirzepatide is a dual agonist. It activates the GLP-1 receptor and the GIP (glucose-dependent insulinotropic polypeptide) receptor. GIP is a second incretin hormone, and adding its activity appears to enhance the metabolic effect — improving insulin sensitivity and, in some analyses, affecting fat metabolism more directly than GLP-1 activity alone.

That second receptor is the entire mechanistic difference, and it is why tirzepatide has generally outperformed semaglutide on weight outcomes.

What the Trials Show

Important: Trial averages describe populations, not people. Within any trial, some participants lose 30% and some lose almost nothing. The average difference between these drugs is smaller than the variation between individuals taking the same one. Do not treat "tirzepatide is better" as a prediction about you.

Both trial programmes paired medication with a reduced-calorie diet and increased physical activity. The medication was never tested in isolation, and the licensed indications reflect that.

Side Effects Compared

The side effect profiles are broadly similar because both act on the same GLP-1 pathway. The most common adverse effects for both are gastrointestinal:

• Nausea, particularly during dose escalation
• Vomiting and diarrhoea
• Constipation
• Abdominal pain and reflux
• Reduced appetite to the point of inadequate intake in some patients
• Fatigue and dizziness, often secondary to eating too little

Serious but less common risks for both include pancreatitis, gallbladder disease (including gallstones), and, in people with existing diabetic retinopathy, potential worsening with rapid glucose improvement. Both carry a boxed warning relating to thyroid C-cell tumours observed in rodents; both are contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN2 syndrome.

Our side effects guide covers management in detail, and managing side effects of GLP-1 therapy covers practical strategies.

Cost Considerations

Cost frequently decides this question before efficacy does.

In the United States, manufacturer self-pay channels set the floor. Novo Nordisk's NovoCare® Pharmacy launched Wegovy at $499 per month cash for all dose strengths, with reporting subsequently describing $349 per month for Wegovy and Ozempic through its direct-to-consumer programme. Eli Lilly's LillyDirect has published Zepbound vial pricing of $349 for 2.5 mg, $499 for 5 mg and 7.5 mg, $599 for 7.5 mg refills after 45 days, and $699 for 10 mg.

Note the structural difference: Novo's flat pricing across strengths means escalating costs you nothing extra, while Lilly's tiered pricing penalises higher doses. If you expect to need a high dose, that changes the arithmetic considerably.

In the UK, private pricing generally starts between about £129 and £200 at the lowest dose and rises to roughly £299–£339 at the highest strengths, with Wegovy often cheaper than Mounjaro at equivalent programme tiers. See our UK cost guide.

Which Should You Choose?

Tirzepatide may suit you better if:

• Maximum weight loss is the priority and cost is manageable
• You have insulin resistance or type 2 diabetes where the dual mechanism may help
• You have tried semaglutide without adequate response
• You can access flat or affordable pricing at higher doses

Semaglutide may suit you better if:

• Cost is a primary constraint and semaglutide is cheaper in your channel
• You want the option of an oral formulation
• Availability of tirzepatide is constrained where you are
• You have cardiovascular disease, where semaglutide has substantial outcome data

Pro Tip: The best drug is the one you can afford and tolerate for long enough to work. A patient who stays on semaglutide for 18 months will almost always do better than one who takes tirzepatide for three months and stops because of cost or nausea.

Switching Between Them

Switching is common and clinically routine, usually in one of three situations: inadequate response, intolerable side effects, or supply and cost problems. Some UK providers publish specific switching guidance — ZAVA, for example, indicates that patients on 7.5 mg or higher of Mounjaro can usually move to the maximum maintenance dose of the Wegovy pill.

Switching is not a matter of matching milligrams. The doses are not equivalent, and your prescriber will set a starting point based on your current dose and tolerance. Never self-manage a switch.

Frequently Asked Questions

Is tirzepatide better than semaglutide?

On average, tirzepatide has produced greater weight loss in clinical trials — roughly 16.5% to 22.4% over 72 weeks depending on dose, versus around 15% at 68 weeks for semaglutide 2.4 mg. However, individual variation is large, and factors such as cost, tolerability, and availability often matter more in practice than the average difference.

What is the difference between Wegovy, Ozempic, Mounjaro, and Zepbound?

Wegovy and Ozempic both contain semaglutide; Wegovy is approved for weight management and Ozempic for type 2 diabetes. Zepbound and Mounjaro both contain tirzepatide; Zepbound is approved for weight management and Mounjaro for type 2 diabetes.

Do they have different side effects?

The profiles are broadly similar because both act on the GLP-1 pathway. Nausea, vomiting, diarrhoea, and constipation are the most common for both, most pronounced during dose escalation. Individual tolerance varies, and some patients tolerate one considerably better than the other.

Is there an oral version of either?

Oral semaglutide is available as the Wegovy Pill. There is no oral tirzepatide; Eli Lilly's oral GLP-1 is a different molecule, orforglipron, marketed as Foundayo.

Which is cheaper?

It depends entirely on your channel and country. In the US, Novo Nordisk's flat self-pay pricing across dose strengths can make semaglutide cheaper at higher doses, while Lilly's tiered vial pricing starts lower at 2.5 mg. In the UK, Wegovy is often the cheaper option at equivalent programme tiers.

Can I switch from one to the other?

Yes, and it is clinically routine when response is inadequate or side effects are intolerable. Doses are not directly equivalent between the two, so a prescriber must set your starting dose after a switch. Never adjust this yourself.

Bottom Line

Tirzepatide's dual GIP/GLP-1 mechanism has produced greater average weight loss in trials, and if maximum efficacy is your goal and you can afford and tolerate it, it is the stronger starting point. Semaglutide remains highly effective, has more extensive cardiovascular outcome data, offers an oral option, and is often cheaper — particularly at higher doses where flat manufacturer pricing applies.

The far more important variables are whether you can sustain the cost, whether you tolerate the titration, and whether you have the support to stay on treatment. Those determine outcomes more than the molecule does.

CoreAge Rx offers both semaglutide and tirzepatide with all-in monthly pricing from $179–$399 including medication, provider messaging, and titration support. 12–24 hour approvals. Save up to $200 on your first three months.

Medical disclaimer: Informational only, not medical advice. Semaglutide and tirzepatide are prescription medicines with real risks, contraindications, and a boxed warning regarding thyroid C-cell tumours. Consult a qualified healthcare professional before starting, switching, or stopping treatment.

Sources: FDA prescribing information for Wegovy, Ozempic, Zepbound, and Mounjaro; NICE obesity management guidance; NovoCare® and LillyDirect published self-pay pricing; European Medicines Agency product information.

Date reviewed: August 2026