GLP-1 medicines for weight: what to know and questions to ask

How do they work?

GLP-1 (glucagon-like peptide-1) is a hormone your gut releases after eating. These medicines mimic it, which:

• reduces appetite and "food noise";
• slows how quickly the stomach empties, so you feel full for longer;
• helps the body release insulin when blood sugar is high.

Some newer medicines in this group act on more than one hormone. Most are given as a weekly or daily injection; some come as tablets.

Who might they be suitable for?

The WHO guideline (December 2025):

• makes a conditional recommendation for adults with obesity (BMI of 30 or more), excluding pregnant women;
• recommends they be combined with intensive behavioural support (nutrition, activity and follow-up);
• describes obesity as a chronic, relapsing disease needing long-term care;
• notes that long-term safety data are still limited, and warns about counterfeit products.

Product labelling in many countries also allows use at a lower BMI when there are weight-related conditions. Your doctor will consider your overall health, other medicines and goals.

Who should not use them (or needs extra care)?

According to NHS guidance, these medicines are generally not suitable if you are:

• pregnant, trying to conceive or breastfeeding;
• someone with a history of pancreatitis;
• someone with type 1 diabetes, or certain other conditions.

They also need extra care in people with some thyroid cancers in the family, gallbladder disease, a history of eating disorders, or severe gut problems. Some can affect how well oral contraceptives work, so ask about contraception.

Common side effects

The most common side effects are:

• nausea, and sometimes vomiting;
• constipation or diarrhoea;
• reflux, bloating and reduced appetite;
• headache and tiredness.

They are often worse when starting or increasing the dose, and usually ease over time. Rare but serious problems include pancreatitis and gallbladder problems.

Seek urgent medical care for severe, persistent abdominal pain (especially going through to the back), persistent vomiting, signs of dehydration, or yellowing of the skin or eyes.

Protecting your muscle

Rapid weight loss includes some loss of muscle. To protect it:

• eat enough protein at each meal;
• do strength training at least twice a week;
• stay active and drink enough fluids.

What happens if you stop?

Weight regain is common. In a follow-up of a large trial, people who stopped treatment regained about two-thirds of the weight they had lost within a year. This doesn't mean the medicine "failed"; it reflects that obesity is a chronic condition. Plans for the long term, including stopping, should be made with your doctor.

Stay safe: avoid unregulated sources

Only use these medicines when prescribed by a doctor and dispensed by a registered pharmacy. Products sold online, through social media, at salons or as "compounded" versions may be fake, contaminated or wrongly dosed. The WHO has warned specifically about counterfeit products.

Questions to ask your doctor

1. Am I a suitable candidate, given my health and other medicines?
2. What results are realistic for me, and how will we measure success beyond the scale?
3. What side effects should I watch for, and what should I do if they happen?
4. How will we protect my muscle mass?
5. What support will I get with eating, activity and sleep?
6. How long would I take it, and what's the plan if I stop?
7. What about contraception, pregnancy plans or breastfeeding?