GLP-1 medicines: important safety advice

Last Updated: Monday, 12 October 2026

These medicines treat type 2 diabetes and, for some products, help manage weight. Examples include:

• Semaglutide: Ozempic, Rybelsus and Wegovy.
• Tirzepatide: Mounjaro.
• Liraglutide: Saxenda.
• Dulaglutide: Trulicity.

They help control blood sugar. Some also reduce appetite and slow the movement of food through your stomach.

Common side effects

Feeling sick, vomiting, diarrhoea and constipation are common, particularly when starting treatment or increasing the dose.

Drink regularly to avoid dehydration, following any fluid limits your clinician has given you. Seek medical advice promptly if you cannot keep fluids down, are passing much less urine or feel very dizzy.

Low blood sugar can also occur, especially if you take insulin or certain other diabetes medicines. Watch for sweating, shaking, hunger or confusion and follow your agreed treatment advice.

Severe tummy pain: seek urgent help

These medicines can cause pancreatitis, which is inflammation of the pancreas. It can sometimes be severe or life-threatening.

Stop taking the medicine and seek urgent medical help if you have severe tummy pain that does not go away, especially if it spreads to your back. You may also feel sick or vomit.

Do not assume this is a normal side effect. Do not restart the medicine if pancreatitis is confirmed.

Semaglutide: sudden changes in eyesight

Semaglutide has been linked to a very rare eye condition called NAION, which can cause sight loss.

Go urgently to eye casualty or A&E if you suddenly lose some or all of your sight, or your eyesight worsens quickly. This can happen without pain. Tell the clinician you take semaglutide.

Contraception and pregnancy 

Use effective contraception during treatment. These medicines should not be used during pregnancy.

If you take Mounjaro and the contraceptive pill, use condoms as well:

• For 4 weeks after starting Mounjaro, including when switching from another medicine.
• For 4 weeks after every dose increase.

Alternatively, discuss contraception that is not taken by mouth, such as a coil, implant, injection, patch or ring.

Other GLP-1 medicines have not been shown to directly reduce the pill’s effectiveness. However, vomiting or severe diarrhoea can affect the pill. Follow your pill’s missed-pill instructions and ask a pharmacist or contraception service for advice.

If you need emergency contraception, tell the clinician or pharmacist which medicine you take.

Speak to your prescriber before trying for a baby. Semaglutide should be stopped at least 2 months, and tirzepatide at least 1 month, before a planned pregnancy. Contact your prescriber promptly if you become pregnant.

If you use HRT

Tell your HRT prescriber before starting these medicines or increasing the dose.

They may affect the absorption of HRT tablets, although evidence is limited. If you have a womb, the progesterone or progestogen part of HRT protects its lining, so your treatment may need reviewing.

Your clinician may recommend a different dose or a method that is not taken by mouth, such as a suitable hormonal coil or combined HRT patch. Do not change your HRT dose yourself. Report new or unexpected vaginal bleeding.

Use your medicine safely

• Use only the prescribed dose.
• Obtain treatment through a registered prescriber and pharmacy.
• Avoid buying medicines through social media or unverified sellers.
• Tell your GP about any privately prescribed treatment.

Want to discuss your treatment?

Contact your GP practice to book a medication review with a clinician, including questions about side effects, contraception or HRT.

Further information

• MHRA: side effects and safe use
• MHRA: pancreatitis warning
• MHRA: semaglutide and eyesight
• Patient leaflet: GLP-1 medicines and contraception