Weight loss injections: what to consider before starting IVF

Weight loss drugs like Wegovy, Ozempic, and Mounjaro are now widely prescribed across the UK. Originally developed for managing type 2 diabetes, they’re increasingly used to support weight loss—especially for those who have a higher BMI and polycystic ovary syndrome (PCOS) or those advised to reduce their BMI before starting fertility treatment. 

But what impact do these medications have on fertility? Are they safe to take when trying to conceive? And if they’re not, what are the alternatives? 

Weight, fertility, and treatment eligibility 

Higher body weight can affect fertility in several ways.  A raised BMI can disrupt the hormones that control ovulation, making periods irregular or absent altogether. It may also reduce how the body responds to fertility drugs, which can affect how the ovaries respond to medication during IVF. 

In people with testes, a higher BMI can reduce sperm count and motility, while also affecting hormone balance. 

There are also treatment access considerations: 

• NHS-funded IVF usually requires a BMI under 30 

• At Care Fertility, we offer private treatment to individuals with a BMI up to 35 

These limits are based on clinical safety. A higher BMI can increase risks during sedation, the egg collection procedure and pregnancy. 

How weight loss medications work 

In the UK, there are several licensed GLP-1 medicines including semaglutide (sold under the brand names Wegovy, Ozempic and Rybelsus), tirzepatide (Mounjaro) and liraglutide (sold under various brand names). “Licensed” means they have been assessed carefully by the UK medicines regulator, the Medicines and Healthcare products Regulatory Agency (MHRA), and approved as safe and effective for certain uses, outlined in the table below. 

GLP-1s are medicines licensed to treat specific medical disorders and should only be used if you are overweight or diabetic, and not if you want to lose weight for aesthetic or cosmetic purposes. 

The most common weight loss drugs in the UK are: 

• Wegovy (semaglutide) - Licensed for weight loss management alongside reduced calorie diet  

• Ozempic (semaglutide) – Licensed to treat diabetes Ozempic can also be prescribed ‘off-label’ to for weight loss 

• Mounjaro (tirzepatide) – Licensed for both treatment of diabetes and weight loss management alongside reduced calorie diet in people with obesity or people who are overweight with weight related health problems  

• Rybelsus (Semaglutide) - Licensed to treat diabetes Rybelsus can also be prescribed ‘off-label’ to for weight loss 

All three drug mimic hormones that help regulate appetite, digestion. Mounjaro also acts on the signalling system that controls blood sugar levels and insulin sensitivity. Taken once a week as an injection, they: 

• Slow down how quickly the stomach empties, helping you feel full for longer 

• Reduce hunger signals in the brain, decreasing appetite 

• Improve insulin sensitivity, which can help regulate hormones in people with insulin resistance or PCOS 

They can support gradual weight loss over several months and may lead to improvements in ovulation and menstrual regularity, especially in those with PCOS. Some research suggests they may help restore cycles in people who were previously not ovulating at all. 

Are they safe during fertility treatment? 

The Medicines and Healthcare products agency (MHRA), have recently (June 2025), released the following guidance: 

No. These medications are not considered safe to use when trying to conceive, either naturally or via IVF, in pregnancy or breast feeding.  

There’s a lack of long-term safety data for use in people undergoing fertility treatment or in pregnancy. Animal studies have shown potential risks to early development, and human studies are limited. Because of this, the current recommendation is to stop taking weight loss medication at least eight weeks before starting fertility drugs or attempting to conceive*. 

This is at least 1 month for Mounjaro, and at least 2 months for Wegovy, Ozempic, and Rybelsus. 

This period after stopping taking the medication is called the ‘wash out’ window, in which your body gets rid of any remaining drugs in your system. Following this guidance ensures accurate hormone testing and avoids any potential interactions with fertility medication. 

What to do after stopping weight loss injections 

If you’ve been prescribed a weight loss drug and are preparing for fertility treatment, it can be difficult to maintain weight loss momentum during the ‘washout’ window. But there are safe and effective alternatives that can help you stay on track without medication: 

• Nutritional support: A balanced, lower-glycaemic diet can help maintain steady blood sugar and reduce cravings. A nutritionist experienced in fertility can provide tailored advice. 

• Regular movement: Moderate activity such as walking, swimming or gentle strength training can help regulate insulin, boost energy and reduce inflammation. 

• Monitoring and motivation: Simple tools like food diaries, step counters or support groups can help you feel more in control during this transition. 

• Stress management: Elevated stress can impact hormones linked to both weight and fertility. Practices like mindfulness, yoga or CBT can help regulate the body's stress response. 

It’s important to avoid crash dieting or extreme restrictions, especially just before or during IVF. These can do more harm than good, potentially affecting hormone levels. 

Can these drugs support fertility in the long term? 

Possibly. For some individuals, particularly those with PCOS or insulin resistance, GLP-1 and GIP/GLP-1 medications may support hormonal regulation and restore ovulation. For others, the benefit may be primarily related to overall weight loss. 

However, these drugs are not currently licensed as fertility treatments, and their use should be managed carefully in the context of your reproductive goals. 

In summary 

• GLP-1 drugs like Wegovy, Ozempic and Mounjaro can support weight loss and may help with cycle regulation in some people. 

• They are not safe to use whilst trying to conceive e.g. during IVF or pregnancy and breastfeeding. You should stop them at least four to eight weeks (depending on which weight-loss medication you are using) before starting fertility medication. 

• Safe, sustainable weight management strategies can be used during that time, and throughout treatment. 

• If you’re considering or currently taking one of these medications, it’s important to speak to a doctor before starting or stopping. 
  

Have questions about weight loss medication and fertility? 

Speak to your GP or fertility specialist for personalised advice based on your medical history and treatment plan. If you're planning IVF, it's best to bring up any medication use early, so your care can be tailored safely around your goals. 

*At the time of writing (July 2025) this was the guidance provided by the Medicines and Healthcare products agency (MHRA).