Semaglutide: Ozempic, Wegovy and Rybelsus explained

Semaglutide copies a natural gut hormone called GLP-1. The NHS describes how it affects appetite and digestion: for weight management it reduces appetite and helps you feel full for longer, while for diabetes it lowers blood sugar, prompts the body to make insulin when needed and slows digestion so that blood sugar is steadier after meals.

The NHS lists three UK brands. Wegovy is the obesity product, and Ozempic and Rybelsus are for type 2 diabetes. It may also be offered to some people with overweight or obesity who have had a cardiac event or have peripheral arterial disease. Decisions about who should use it, on the NHS or privately, belong to a qualified prescriber after assessment.

The weight-management and diabetes injections are self-administered once a week, on the same day each week with at least three days between doses, into fatty areas such as the thigh, abdomen or upper arm, with sites rotated. The emc product information for Ozempic describes a stepwise increase over several weeks starting with a lower dose that it states is not a maintenance dose.

Rybelsus follows a different routine. The NHS says to take it on waking, having not eaten for the previous eight hours, swallowed whole with a small amount of water (up to about a hundred and twenty millilitres), then wait thirty minutes before eating, drinking or taking other medicines. That routine matters because food and drink interfere with absorption.

For the weekly injection the NHS says that if you are no more than five days late, inject as soon as you remember; if later than that, skip the missed dose and resume your usual day. For the tablet, skip the missed dose and carry on normally. Never double up.

Talk to your prescriber before stopping. The NHS notes that a gradual dose reduction may be recommended, particularly in diabetes.

The NHS lists feeling sick and being sick, constipation, diarrhoea, tiredness, itchy or red skin where you inject, and hair loss. The emc information for Ozempic describes gastrointestinal effects as typically mild to moderate and short lived, most frequent in the first months, and warns that vomiting or diarrhoea can cause dehydration that affects the kidneys.

Serious problems include allergic reactions, acute pancreatitis (persistent severe stomach pain), low blood sugar when combined with other diabetes medicines, worsening diabetic retinopathy, and sudden vision loss. The emc information reports a rare optic nerve condition called NAION and asks for urgent eye referral if vision is suddenly lost. Contact NHS 111 if you think you are having a serious effect, and 999 for anaphylaxis.

• Persistent severe stomach or back pain: seek urgent advice.

• Sudden loss or change of vision: seek urgent advice.

• Swelling of the throat or tongue with breathing difficulty: call 999.

The NHS says semaglutide is not suitable if you are allergic to it or other GLP-1 medicines, or have had acute pancreatitis. The emc information adds caution for people with diabetic retinopathy, particularly those on insulin, because rapid improvement in glucose can temporarily worsen eye disease.

The NHS says semaglutide is not used while breastfeeding because it passes into breast milk, and it is not used in pregnancy. It advises stopping at least two months before attempting conception and using contraception if pregnancy is possible during treatment.

The NHS names warfarin, levothyroxine, insulin, metformin, gliclazide and anaesthetic or sedative agents as medicines that may interact or need dose changes. The emc information says slowed stomach emptying may affect medicines needing quick absorption and that anaesthetists should know you use a GLP-1 medicine because of aspiration risk. The NHS advises avoiding alcohol as it increases sickness. Avoid driving if you feel dizzy or have vision problems.

Semaglutide is a prescription-only medicine. Suspected side effects can be reported through the Yellow Card scheme.