Yes, weight loss injections can impact fertility, but not always as people think. For some women with PCOS or obesity-related hormonal issues, GLP-1 meds like Wegovy and Mounjaro can help restore ovulation. This can boost the chances of natural conception. These medications are generally not recommended during pregnancy. Tirzepatide may temporarily make oral contraceptives less effective.

Men are affected too. Testosterone levels and sperm quality often change as weight drops. The picture is more layered than a simple yes or no. 

Read on to understand what the research actually shows and what to do if fertility is on your radar.

How Do Weight Loss Injections Work?

Mounjaro (tirzepatide) and Wegovy (semaglutide) belong to a drug class called GLP-1 receptor agonists. GLP-1 is a hormone your gut already produces naturally after eating, and these medications mimic it.

They signal your brain to feel full, slow down digestion, and help the body manage blood sugar more efficiently. The result is reduced appetite and, over time, meaningful weight loss. Our Weight Management service can provide personalised support for people looking to manage their weight with safe, evidence-based treatment options.

As body fat decreases and insulin sensitivity rises, hormonal systems that were once out of balance start to stabilize. That metabolic shift is where the fertility connection starts.

Why Is It Important to Maintain a Healthy Weight for Fertility?

Excess body fat disrupts the hormonal balance needed for healthy reproduction in both men and women. Fat tissue changes androgens into oestrogen. This can mess with the signals between the brain and the ovaries or testes.

In women, this commonly leads to irregular periods, poor egg quality, and conditions like PCOS. In men, high body fat is linked to lower testosterone and reduced sperm quality.

Reaching a healthier weight does not guarantee fertility, but it removes one of the most common barriers to it. That is why weight management and reproductive health are so closely connected in clinical practice.

How Weight Loss Injections Can Boost Female Fertility

The PCOS Connection

PCOS (Polycystic Ovary Syndrome) is one of the leading causes of female infertility in the UK. Insulin resistance and extra body weight are closely linked. Both can mess with the hormones that start ovulation.

When insulin levels stay too high, the ovaries produce more androgens than normal. Excess androgens can prevent eggs from maturing properly and can halt the menstrual cycle entirely. Many women with PCOS stop ovulating, which makes natural conception very difficult.

GLP-1 medications address this directly. They improve insulin sensitivity and support weight loss. This helps reduce androgen excess and allows the reproductive system to return to its natural rhythm.

Restoring the Menstrual Cycle

Losing 5 to 10 per cent of body weight can restart regular ovulation in women who have stopped cycling. It does not require a dramatic transformation to see real results.

Women on Mounjaro or Wegovy often report that their periods return after months or even years of absence. This might show the impact of weight loss and better metabolic health. However, more research is needed to confirm a direct effect from the medication.

Fertility specialists often talk about weight management before suggesting IVF or other treatments because weight loss can sometimes restore ovulation. When the body moves closer to its natural hormonal balance, it tends to do what it was designed to do.

Why Weight Loss Injections Are Leading to Unexpected Pregnancies

The Social Media Trend

You may have seen the phrase “Ozempic babies” online. It refers to women who struggled with infertility for years. They started a GLP-1 medication and then became pregnant unexpectedly. In the UK, Ozempic is approved only for treating type 2 diabetes. It is not for weight management.

This is not purely a social media story. Fertility clinics in the UK and US have seen more unplanned pregnancies in women using these medications. The mechanism is straightforward: restored ovulation in women who believed they were infertile.

For some, this is genuinely good news. For women who are not ready for pregnancy, it is a serious prompt to revisit contraception.

Do Weight Loss Shots Cancel Out Birth Control?

This applies specifically to Mounjaro. If you take the oral contraceptive pill and get Mounjaro, use barrier methods for protection. You can also switch to a non-oral method, such as the coil or implant.

Do this for four weeks after starting and for four weeks after each dose increase. Dose increases happen roughly monthly at first. For Wegovy and other semaglutide treatments, there isn’t strong evidence that the pill works well. However, severe vomiting or diarrhoea from these medicines can lower absorption as usual.

Do Weight Loss Injections Affect Male Fertility?

Men are often left out of this conversation, but they should not be.

The Hormone Balance

Excess body weight in men raises oestrogen and lowers testosterone. This matters because testosterone is essential for sperm production. When levels drop significantly, sperm count, motility, and morphology can all be affected.

Obesity also raises scrotal temperature, which independently reduces sperm quality. Male factor infertility accounts for about half of all couples facing difficulty in conceiving. This is a significant issue.

Emerging Research

Early data on GLP-1 therapy in men is encouraging. Clinical observations and smaller studies suggest that men who lose weight on semaglutide or tirzepatide often show improvements in testosterone levels and sperm parameters.

This research is still in early stages, and large long-term trial data is not yet available. But the biological reasoning is sound: as metabolic health improves, reproductive health tends to follow. Men who are trying to conceive should raise this with their doctor when discussing weight management options.

Weight Loss Injections and Pregnancy

The Medical Consensus

GLP-1 medications are not recommended during pregnancy. This is clear guidance from the MHRA and the manufacturers. If you find out you’re pregnant while using Mounjaro or Wegovy, stop taking the medication. Then, contact your GP or prescriber right away. You do not need to wait for an appointment, and you do not need to taper. Simply do not take the next injection.

Furthermore, GLP-1 medications are contraindicated during breastfeeding. They aren’t in Patient Group Directions (PGDs) due to a lack of safety data on their presence in breast milk.

What the Data Says

Human registry data from 2025 and 2026 is reassuring. This data shows that major birth defects in women exposed early in pregnancy are less concerning, even if they didn’t know they were pregnant. Animal studies have shown that doses similar to those used in humans can affect fetal development.

The honest position is that we do not yet have enough long-term human data. These medications are too new for anyone to say with full confidence what the risks are across all pregnancy outcomes. Caution remains the right approach.

The “Washout” Period

UK guidance from the MHRA sets different washout periods depending on your medication. If you are taking Mounjaro (tirzepatide), stop at least one month before trying to conceive. If you are taking Wegovy or another semaglutide treatment, stop at least two months before. The difference reflects how long each drug takes to clear. Don’t stop suddenly. Talk to your prescriber first. They will help plan your weight and metabolic health during the change.

Folic Acid

One thing to start before you stop the medication, not after. Anyone trying to conceive should take folic acid every day. Start before conception and continue until 12 weeks of pregnancy. The standard dose is 400 micrograms. If your BMI is 30 or higher, the recommended dose is 5 mg. This requires a prescription, not an over-the-counter supplement. Ask your GP or pharmacist when you plan your washout.

Stopping Weight Loss Medication Before Fertility Treatment

If you’re getting ready for IVF or another fertility treatment, your specialist will likely ask you to stop GLP-1 medications first.

The main concern is that these drugs haven’t been tested in fertility treatments. The impact of these drugs on egg retrieval, embryo quality, and ovarian response to stimulation drugs is not clear.

Nausea and vomiting are common side effects of GLP-1 therapy. This can make it hard to take oral medications during IVF cycles. Stopping at least two months beforehand gives your body time to stabilise before treatment begins.

Talk to both your fertility team and your prescriber well in advance. The timing matters more than most people initially realise.

Possible Side Effects That May Indirectly Affect Fertility

Beyond the direct effects discussed above, a few indirect factors are worth knowing.

Nausea and a loss of appetite can create nutritional gaps over time. This is especially true if diet isn’t managed well. Folate, zinc, and iron are all important for reproductive health, and low levels can affect both egg quality and sperm production.

Rapid weight loss can temporarily disrupt the menstrual cycle in women who are at a healthy weight. If your periods become irregular after starting a GLP-1 medication, raise it with your GP.

These are manageable issues, not reasons to skip treatment. Still, it’s good to keep them in mind.

What Does Current Research Say?

The research is moving quickly, but it has not yet caught up with the number of people taking these medications. The gap between what we know and what we need to know is still meaningful.

For more information, check the NHS guidance on medicines in pregnancy. It explains how medications are evaluated for safety during pregnancy in the UK.

Frequently Asked Questions

Can I continue weight loss injections while actively trying to conceive? 

No. Current advice says to stop GLP-1 medications at least eight weeks before trying to conceive. These medications are not safe in early pregnancy.

Does Mounjaro specifically damage egg quality in women with PCOS?

There is no direct evidence that tirzepatide harms egg quality. Losing weight can improve metabolic health. This may help egg development by lowering the high androgen levels often seen in PCOS.

How quickly can ovulation return after starting a GLP-1 medication? 

Ovulation can return in weeks or a few months. Sometimes, it happens even before weight loss. This is because early gains in insulin sensitivity affect hormone signalling.

Should men stop weight loss injections before a partner undergoes IVF? 

There is no specific published guidance on this. Some clinicians suggest pausing for three months before IVF. This time allows for a complete sperm renewal cycle, which takes about 72 to 90 days.

Are weight loss injections used as a fertility treatment? 

No. GLP-1 medications are not licensed as fertility treatments. Any reproductive benefit comes from weight loss and better metabolic health. It does not result from the drug acting directly on the reproductive system.

Conclusion

Weight loss injections can affect fertility in several meaningful ways. Women with PCOS or obesity-related hormone issues can restore ovulation. This can greatly improve their chances of conceiving naturally. For men, losing weight on GLP-1 therapy may improve testosterone and sperm quality.

These medications aren’t safe to use during pregnancy. They can also make oral contraception less reliable. If you’re thinking about pregnancy while on these drugs, have a clear plan. Include the suggested washout period before you try to conceive.

The research is still developing. If fertility is part of your plans, speak to your GP or a specialist before making any changes to your medication. Getting the timing right is what makes the difference.