GLP-1 Medicines: Semaglutide, Tirzepatide and Liraglutide

What GLP-1 medicines are

GLP-1 medicines are prescription peptide drugs that copy a gut hormone called glucagon-like peptide-1. They were developed for type 2 diabetes, and some are also approved for weight management. NHS describes semaglutide, liraglutide and tirzepatide as GLP-1 (or GLP-1/GIP) medicines that reduce appetite and slow digestion. [1][2][3] A 2025 review states that liraglutide, semaglutide and tirzepatide are FDA-approved for obesity treatment. [4] Evidence label for all three: approved medicine (FDA in the U.S.; the NHS pages describe UK use). This page covers prescription medicines only: it gives no amounts, no sourcing and no advice to start, stop or change a medicine. Talk with the prescriber.

Semaglutide

Brand names in the UK include Wegovy for weight and Ozempic and Rybelsus for type 2 diabetes. [1]

• Weight trial. In STEP 1, 1,961 adults with overweight or obesity and no diabetes were treated for 68 weeks alongside lifestyle support. Average weight change was -14.9% with semaglutide versus -2.4% with placebo. Nausea and diarrhea were the most common adverse events, and 4.5% stopped because of stomach and gut effects versus 0.8% on placebo. [5]
• Heart outcomes. In SELECT, 17,604 adults aged 45 or older with existing cardiovascular disease and overweight or obesity but no diabetes had a major cardiovascular event in 6.5% on semaglutide versus 8.0% on placebo (hazard ratio 0.80). Permanent stopping because of adverse events was 16.6% versus 8.2%. [6]

Tirzepatide

Tirzepatide acts on both GLP-1 and GIP receptors. [3] The FDA approved Zepbound (tirzepatide) for chronic weight management on November 8, 2023, and noted it was already approved as Mounjaro for type 2 diabetes. [7]

• Weight trial. In SURMOUNT-1, 2,539 adults without diabetes were treated for 72 weeks. Average weight change at the three tested strengths ranged from -15.0% to -20.9%, compared with -3.1% on placebo. Most common adverse events were gastrointestinal, mostly mild to moderate and mainly during dose escalation. [8]

Liraglutide

Liraglutide is used for type 2 diabetes (UK brands Diavic and Zegluxen) or obesity (Saxenda), and is injected once a day. [2]

• Weight trial. In SCALE, 3,731 adults without type 2 diabetes were treated for 56 weeks: average loss was 8.4 kg versus 2.8 kg with placebo. Serious events occurred in 6.2% versus 5.0%. [9]

What the trials do and do not show

STEP 1 and SCALE were funded by Novo Nordisk and SURMOUNT-1 by Eli Lilly, the makers of the drugs. [5][9][8] Weight outcomes were for people with a BMI in the studied range using the drug alongside lifestyle support. Results are averages; individual results vary. The trials above cannot tell you what happens after stopping or over many years. Label: established for short- to medium-term weight reduction in these populations.

Risks, cautions and special groups

• Common side effects (NHS): nausea, vomiting, constipation, diarrhea, tiredness, and injection-site itching or redness. [1] Tirzepatide also lists stomach pain and hair loss. [3]
• Serious but rare (NHS): allergic reaction, inflamed pancreas, worsening diabetic eye disease (semaglutide), low blood sugar especially with other diabetes medicines, and gallstones or gallbladder inflammation with tirzepatide and liraglutide. [1][3][2]
• Thyroid warning. The FDA's Zepbound announcement says thyroid C-cell tumors occurred in rats; it is unknown whether this happens in humans, and the drug should not be used with a personal or family history of medullary thyroid cancer or MEN 2. [7]
• Pregnancy and breastfeeding. The NHS says there is not enough information to say these medicines are safe in pregnancy, and gives specific guidance on timing before trying to conceive, so ask your prescriber. [1][3] Semaglutide is not used while breastfeeding. [1]
• Not for combining. Zepbound should not be used with Mounjaro or another GLP-1 drug. [7]
• Fake products. The NHS warns some websites sell fake weight-loss medicines. [1] See compounded and unapproved GLP-1 products.

Seek urgent medical help for severe, persistent stomach or back pain, swelling of the throat or tongue, or trouble breathing. [1]

Related guides

Weight-loss medications and medical care, weight safety and when to get help, medication interactions and what peptides are.