Weight-loss drugs (GLP-1): semaglutide, tirzepatide, liraglutide

What are GLP-1 drugs?

GLP-1 (glucagon-like peptide 1) is a hormone made in the gut. GLP-1 receptor agonists act like it in the body. They increase the insulin released by the pancreas after a meal and regulate appetite: the feeling of fullness increases and hunger decreases [9, 10, 13]regulator.

Besides GLP-1, tirzepatide acts like a second gut hormone, GIP (glucose-dependent insulinotropic polypeptide) [12]regulator. The investigational drug retatrutide acts on three receptors: GIP, GLP-1 and glucagon [8]A.

Semaglutide and tirzepatide are injected once a week, and liraglutide once a day. Semaglutide is also available as a once-daily tablet [10, 11, 12, 13]regulator.

Read more: What a weight-loss drug costs and how to get one (prices, Kela, prescription) | Upcoming weight-loss drugs: orforglipron, CagriSema, retatrutide

Which is which: Ozempic, Wegovy and Rybelsus (semaglutide), Mounjaro (tirzepatide), Saxenda, Victoza and Ablymico (liraglutide)

The same active substance can be sold under several brand names for different uses. The table shows what each product is authorised for in the EU and how it is given. All authorised products in the table are available only with a prescription [9, 10, 11, 12, 13, 14, 21]regulator. Ablymico was not in the medicines search of Kela (the Social Insurance Institution of Finland, which pays medicine reimbursements) on 13 Oct 2026 [25]regulator.

Read more: Semaglutide (Ozempic, Wegovy, Rybelsus) | Tirzepatide (Mounjaro) | Liraglutide (Saxenda, Victoza) | Retatrutide | Cagrilintide and CagriSema

Mounjaro vs Ozempic: what is the difference?

How they work: Ozempic's substance, semaglutide, acts like the gut hormone GLP-1 [9]regulator. Mounjaro's substance, tirzepatide, acts like two gut hormones, GLP-1 and GIP [12]regulator.

Use and how given: Ozempic is authorised for type 2 diabetes in adults [9]regulator, and the weight management product of semaglutide is Wegovy [10]regulator. Mounjaro is authorised both for type 2 diabetes and for weight management in adults [12]regulator. Both are injected under the skin once a week [9, 12]regulator.

Type 2 diabetes: in SURPASS-2, 1,879 people with diabetes received tirzepatide 5, 10 or 15 mg or semaglutide 1 mg a week for 40 weeks. The long-term blood glucose marker HbA1c fell by 2.01 to 2.30 percentage points with tirzepatide and 1.86 percentage points with semaglutide, and weight loss was 1.9 to 5.5 kg greater with tirzepatide [19]A.

Obesity: in SURMOUNT-5, 751 adults without diabetes received the maximum tolerated weekly dose of either tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) for 72 weeks. Body weight fell by a mean of 20.2% with tirzepatide and 13.7% with semaglutide [4]A.

Harms and caveats: in both comparisons the most common adverse events were gastrointestinal, mostly mild to moderate [4, 19]A. Both trials were open-label and funded by the maker of tirzepatide, Eli Lilly. Group averages do not tell which medicine suits an individual [4, 19]A.

Read more: Ozempic vs Wegovy vs Mounjaro: the full comparison | Tirzepatide (Mounjaro) | Semaglutide (Ozempic, Wegovy, Rybelsus)

What trials showed for body weight

Semaglutide: in STEP 1, 1,961 adults without diabetes received 2.4 mg of semaglutide or placebo once a week for 68 weeks alongside lifestyle intervention. Body weight fell by a mean of 14.9% with semaglutide and 2.4% with placebo [1]A.

Tirzepatide: in SURMOUNT-1, 2,539 adults without diabetes received tirzepatide or placebo for 72 weeks. Body weight fell by a mean of 15.0% to 20.9% depending on the dose, and 3.1% with placebo [2]A.

Liraglutide: in SCALE, 3,731 adults without type 2 diabetes received 3.0 mg of liraglutide or placebo once a day for 56 weeks. Body weight fell by a mean of 8.4 kg with liraglutide and 2.8 kg with placebo [3]A.

Head to head: in SURMOUNT-5, 751 adults with obesity but without diabetes received tirzepatide or semaglutide at the maximum tolerated dose for 72 weeks. Body weight fell by a mean of 20.2% with tirzepatide and 13.7% with semaglutide. The trial was open-label [4]A.

Figures from different trials cannot be compared directly, because participants, duration and comparators differed. All four trials were funded by the manufacturer, and the results are group averages, not a promise to any individual [1, 2, 3, 4]A.

Read more: Semaglutide trials | Tirzepatide trials | Liraglutide trials

Most common side effects

According to the EMA, the most common side effects (in more than 1 in 10 people) of the weight management products of semaglutide, tirzepatide and liraglutide are nausea, vomiting, diarrhoea and constipation. With semaglutide and tirzepatide, abdominal pain is also common [10, 12, 13]regulator.

In trials, gastrointestinal symptoms were mostly mild to moderate, and in the tirzepatide and semaglutide trials they occurred mainly while the dose was being raised [1, 2, 4]A. In STEP 1, treatment was stopped because of gastrointestinal events by 4.5% of the semaglutide group and 0.8% of the placebo group [1]A.

Gallstones and gallbladder inflammation were more common than on placebo with all three substances. In the Wegovy trials gallstones occurred in 1.6% and 1.1% on placebo [22]official, in the Mounjaro weight management trials gallbladder inflammation in 0.6% and 0.2% [23]official, and in the liraglutide weight management trials gallstones and gallbladder inflammation were more frequent than on placebo [15]official. Acute pancreatitis has been observed with GLP-1 receptor agonists [15]official.

According to the EMA, semaglutide can worsen diabetic retinopathy [9, 11]regulator. A very rare side effect of semaglutide is also NAION, a circulation disorder of the optic nerve that may affect up to 1 in 10,000 people; sudden loss of vision needs a doctor straight away [24]regulator.

Read more: Weight-loss drug side effects and how they are managed | What users themselves report about side effects | Side effects and how to read them

User experiences

Users’ own accounts, not research. The accounts of semaglutide, tirzepatide, liraglutide and retatrutide users are compiled on this page’s Experiences tab: the number of people, the most often reported benefits and harms, and links to each substance’s own summary.

Read more: Weight-loss drug user experiences

What happens when you stop?

In the STEP 1 extension, 327 participants were followed for a year after semaglutide and the lifestyle intervention ended. The semaglutide group had lost a mean of 17.3% of body weight, and about two thirds of that came back within a year. The net loss from the start was 5.6% [5]A.

In STEP 4, people who had taken semaglutide for 20 weeks were randomly assigned to continue or switch to placebo. Over 48 weeks those who continued lost a further 7.9%, and those switched to placebo regained 6.9% [6]A.

In SURMOUNT-4, people who had taken tirzepatide for 36 weeks were randomised in the same way. Over 52 weeks those who continued lost a further 5.5%, and those switched to placebo regained 14.0% [7]A.

Based on these results, weight often comes back when the medicine is stopped. Talk to your prescriber before stopping [5, 6, 7]A.

Read more: Stopping a weight-loss drug: does the weight come back?

Prescription only: "research use" products online

Semaglutide, tirzepatide and liraglutide are prescription medicines with a marketing authorisation in the EU [9, 10, 11, 12, 13, 14]regulator, and they are named as medicinal substances in the Finnish medicines list [20]regulator.

On 29 June 2026 Fimea warned about injectable peptides sold online and on social media, including products marketed for weight management. According to Fimea, "for research use only" means the product is not intended for humans, and medicines should be bought only from legal pharmacies [16]regulator.

The US Food and Drug Administration (FDA) warns that unapproved GLP-1 products have not been reviewed for safety, effectiveness and quality. The FDA has warned companies that sold semaglutide, tirzepatide or retatrutide falsely labelled "for research purposes" or "not for human consumption". The FDA is also aware of counterfeit Ozempic (semaglutide) and of adverse event reports that may be linked to dosing errors, some requiring hospital care [17]regulator.

Retatrutide is an investigational drug. It is not listed in the EMA medicines database [18]regulator, and according to the FDA it has not been found safe and effective for any condition [17]regulator. In the phase 3 TRIUMPH-1 trial, body weight fell over 80 weeks by a mean of 25.0% at the highest dose (12 mg) and 3.9% with placebo [26]A.

Read more: Weight-loss drugs without a prescription: risks and the law | Peptides and the law in Finland | How to read a certificate of analysis (COA) | Retatrutide