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Women taking GLP-1 receptor agonists (GLP-1 RAs) must use effective contraception, with those taking Mounjaro (tirzepatide; Eli Lilly) requiring a non-oral contraceptive, according to the Medicines and Healthcare products Regulatory Agency (MHRA).
In guidance published on 5 June 2025, the MHRA said that GLP-1 RAs — which include semaglutide, liraglutide and tirzepatide — should not be taken during pregnancy, just before trying to get pregnant or while breastfeeding.
“This is because there is not enough safety data to know whether taking a GLP-1 medicine can cause harm to the baby,” according to the guidance, adding that women on all types of GLP-1 RAs should use effective contraception.
It also advised that those taking tirzepatide (Mounjaro; Eli Lilly) should use a non-oral form of contraception, which is a barrier method, such as a condom or a non-oral contraceptive, such as the coil or implant, for four weeks after starting GLP-1 medicines and for four weeks after any increase in dose.
The MHRA also warned that tirzepatide may reduce the effectiveness of oral contraceptives in those who are overweight or obese.
As a precautionary measure, the guidance advises patients trying to conceive to continue using contraception for a defined “wash-out” period after stopping taking GLP-1 RAs.
Patients taking semaglutide should have stopped using the medication at least two months before trying to conceive, while patients taking tirzepatide should wait at least one month after stopping the medication before trying to conceive, it added.
It also stressed the importance of accessing the medicines from legitimate pharmacies, after a consultation with and prescription from a healthcare professional, and advised patients using a GLP-1 medicine who think they might be pregnant to “speak to a healthcare professional straight away” and stop using the medication as soon as possible.
Commenting on the guidance, Ying Cheong, professor of reproductive medicine at the University of Southampton, said: “With the growing use of GLP-1 receptor agonists among women of reproductive age — often for non-medical, aesthetic weight loss — the MHRA’s reminder is both timely and necessary.
“Gastrointestinal side effects, such as vomiting and diarrhoea, can impair oral contraceptive absorption, increasing the risk of unintended pregnancy. Although direct evidence linking GLP-1 drugs to contraceptive failure is limited, the widespread uptake of these medications means even that small risks could translate into public health concerns, if confirmed in further studies.”
Rebecca Reynolds, professor of metabolic medicine at the University of Edinburgh, said: “It is very important to raise awareness about this MHRA advice among women and clinicians around potential issues with GLP-1 drugs affecting the effectiveness of oral contraceptives in those who are overweight. Many people are buying weight-loss drugs online and so may not receive this important advice about contraception.
“There is hardly any available data from human studies to be able to advise if these weight-loss drugs are safe in pregnancy. The data from animal studies suggests the potential for harm with low birthweight and skeletal abnormalities, though more evidence is needed to assess if there are risks of taking these drugs in humans.”
In the guidance, the MHRA also warned patients against accessing counterfeit weight-loss medication, noting it had received “reports of people experiencing severe side effects from fake GLP-1 medicines”.
“Legitimate GLP-1 medicines are provided in pre-filled injection pens. Products supplied as a powder in vials, which must be mixed with a liquid prior to injection, are not authorised and pose significant health risks,” it said.
Jasmine Shah, medication safety officer at the National Pharmacy Association, said: “Community pharmacies have been experiencing unprecedented levels of interest for weight-loss injections.
“It is, therefore, important that regulations and guidance keep pace with this demand and that patient safety is put at the heart of everything we do.”
She also urged patients to “note this important new guidance from the MHRA published today and use effective contraception”.
“We also reiterate warnings from the MHRA to avoid any potential fake weight loss injections sold on social media or via beauty salons, which could pose a serious risk to someone’s health,” Shah added.
“We urge anyone who has concerns about this medication to speak to their pharmacist for advice.”
In January 2025, the MHRA warned healthcare professionals to be aware of the potential risk of pulmonary aspiration in patients using GLP-1 RAs who undergo surgery or procedures with general anaesthesia or deep sedation.
