Can Wegovy Cause Irregular Periods?

Step 1: understanding why weight loss itself disrupts cycles

A question our prescribers hear most weeks is whether Wegovy has done something to a patient's periods, and the honest answer starts a step back from the medicine. Adipose tissue (body fat) is metabolically active. It produces and stores oestrogen, and when body fat changes quickly, oestrogen levels shift with it. That hormonal fluctuation can lengthen cycles, shorten them, make them heavier or lighter, or temporarily delay them altogether.

Semaglutide (the active ingredient in Wegovy) also improves insulin sensitivity. For women with conditions like polycystic ovary syndrome, where insulin resistance drives hormonal imbalance, that improvement can paradoxically trigger ovulation where there was none before. So some women experience a return of periods they had lost, while others find their previously regular cycle becomes unpredictable. Neither outcome means something has gone wrong, but both are worth tracking. You can read a detailed look at how Wegovy relates to periods more broadly on our dedicated page.

The NHS patient information for semaglutide does not list irregular periods as a listed side effect of the medicine itself, which supports the view that hormonal and metabolic change, rather than direct drug action on the uterus, is the primary driver.

Step 2: the contraception issue that cannot wait

Returning fertility is medically significant. If you were not ovulating regularly before starting Wegovy and your cycle restarts, unintended pregnancy becomes a real possibility. The NHS advises using effective contraception while on semaglutide and for a defined period after stopping, before trying to conceive.

There is a practical wrinkle specific to tirzepatide (Mounjaro) rather than semaglutide: oral contraceptive pills may be absorbed less reliably during the early weeks of tirzepatide treatment because gastric emptying slows. Current NHS guidance does not flag the same absorption concern for semaglutide, but if you are on any hormonal contraception and your cycles are changing in ways that concern you, raising this with your prescriber is sensible. Our page on whether Wegovy can trigger periods covers the fertility-return question in more depth.

The NHS England guidance on weight-management injections addresses contraception explicitly and is the clearest official reference on this point.

Step 3: when to speak to a doctor, not just note it down

Minor cycle variation in the first one to three months of treatment, particularly if your weight is falling steadily, is common and usually self-limiting. Your cycle often stabilises as weight loss slows and your body adjusts to a new hormonal baseline.

The following warrant a conversation with your GP rather than a watch-and-wait approach: periods that stop entirely for more than three months (amenorrhoea); bleeding that becomes significantly heavier or more painful; bleeding between periods; or any changes that cause you distress. These symptoms can have causes entirely unrelated to Wegovy, and a prescriber cannot assess them through a weight-management consultation alone. If you want to understand more about how semaglutide affects periods at different stages of treatment, we have covered that in a separate guide. For a full picture of the medicine itself, our Wegovy overview sets out what it is, how it works, and who it is licensed for in the UK.

When irregular periods settle, and what that means for your treatment

For most women, menstrual irregularity during Wegovy treatment is temporary. As the rate of weight loss levels off (typically after the first few months at a stable maintenance dose), cycles tend to regulate. Some women find their periods are actually more predictable post-treatment than they were before, particularly if weight-driven hormonal disruption had been longstanding.

That said, Wegovy is not licensed or recommended during pregnancy or breastfeeding, and women trying to conceive should discuss timing with both their prescriber and their GP before continuing treatment, and this applies whether you are on a higher dose or still working up from the starting 0.25 mg dose that the 50 mg pen delivers. Under-18s are not licensed to use Wegovy. If you are considering treatment and wondering whether your cycle history might affect eligibility, the starting point is a clinical consultation, our free consultation connects you with a GPhC-registered prescriber who reviews each case individually. You can also explore semaglutide treatment information for a broader clinical overview before you begin.