Wegovy's effects on your period: what we know and what to watch for

You've started Wegovy and your last period arrived ten days early

It catches people off guard. You're a few weeks into treatment, weight is beginning to come off, and your cycle does something unexpected, arriving ahead of schedule, running longer than usual, or feeling heavier than you're used to. The first instinct is to wonder whether the medication itself is interfering. In most cases, the medication is acting indirectly: the change is the body's hormonal system responding to rapid shifts in fat mass, not a pharmacological effect on the uterus or ovaries.

Fat tissue is hormonally active. It produces and stores oestrogen, so when body fat decreases relatively quickly, circulating oestrogen levels can fluctuate. The hormones that trigger ovulation (particularly luteinising hormone (LH) and follicle-stimulating hormone (FSH)) are sensitive to these shifts. The result can be a cycle that feels out of step with its usual rhythm: coming early, arriving late, or varying in flow. Most women find things settle within two to three cycles as the body adjusts to its new hormonal baseline. If yours haven't by month three, that is worth raising with a GP rather than waiting longer.

It is also worth knowing that semaglutide improves insulin sensitivity. For women with insulin resistance (common in obesity and in polycystic ovary syndrome) that metabolic shift can actually help the cycle become more regular over time, not less. The disruption some women notice early on can give way to cycles that are more consistent than they were before treatment started. The broader range of effects reported on Wegovy includes many that are mediated through metabolic change rather than direct drug action, and how Wegovy affects your period specifically is something many women want to understand before that first unexpected cycle change arrives.

The PCOS and fertility dimension: what the weight-loss literature tells us

For women with polycystic ovary syndrome, the relationship between semaglutide and menstrual cycles is genuinely significant. PCOS is closely linked to excess weight and insulin resistance, both of which suppress regular ovulation. Clinical data on GLP-1 medicines in women with PCOS show that meaningful weight loss (the kind Wegovy can produce) can restore or regularise ovulation in women who previously had infrequent or absent periods. NHS England's guidance on weight-management injections specifically flags this: weight loss may restore fertility, sometimes before women expect it, and effective contraception is essential for anyone on Wegovy who does not wish to become pregnant.

That point carries real practical weight. If your periods had been irregular for years, the return of ovulation may not feel obvious, a restored cycle does not announce itself with a text message. For anyone relying on oral contraceptives, there is a separate consideration covered in a moment. The absence of periods on Wegovy and what it means is a related question many women ask, amenorrhoea that predates treatment may actually improve, while cycles that were previously regular occasionally become temporarily unpredictable.

The STEP 1 trial, published in the New England Journal of Medicine, demonstrated average weight loss of around 15% over 68 weeks at the 2.4mg dose. That scale of weight change is significant enough to affect hormonal physiology, which is exactly why cycle changes are so commonly reported in practice even when they sit outside the formal side-effect list in the patient information leaflet.

Oral contraception and Wegovy: the absorption question

Wegovy slows gastric emptying, food and anything you swallow moves through the stomach more slowly than usual. For most medicines that is clinically irrelevant, but for oral contraceptives it raises a practical question about whether the pill is being absorbed reliably. NHS guidance notes there is no strong evidence that semaglutide reduces the effectiveness of the oral contraceptive pill in the way that tirzepatide (Mounjaro) does, where a non-oral backup is recommended for the first four weeks and after each dose increase. For Wegovy, the current position is more cautious: discuss your contraception method with a prescriber or GP, particularly if you take the pill at a time when you might experience nausea or vomiting, since the pill could be lost before absorption.

If you're thinking about the cost of treatment alongside questions like this, our overview of Wegovy pricing explains what a private prescription should include, clinical review, not just a pen in the post. Contraceptive counselling is part of the clinical picture a prescriber considers during your consultation. It is not a box on a form; it is a relevant part of your medical history. A question our prescribers hear most weeks: "Do I need to change my contraception?", and the honest answer is that it depends on which method you use, your cycle history, and where you are in your titration.

For reference, NHS England's page on weight-management injections covers the contraception and fertility guidance in plain terms and is the most direct official source on this question.

When a cycle change needs medical attention

Most menstrual changes in the first two to three months of Wegovy are attributable to hormonal flux from weight loss and will settle. There are situations, though, where a change in your period should prompt a conversation with a GP rather than a wait-and-see approach. Bleeding that is significantly heavier than usual for more than two cycles, spotting between periods, complete absence of periods for three or more consecutive months without a clear prior history of amenorrhoea, or any pelvic pain that feels new, all of these deserve proper assessment. They may be related to weight change, or they may have a cause that has nothing to do with Wegovy and needs investigation in its own right.

You can read more about periods and Wegovy including what other women report. For anything that worries you, the NHS medicines page for semaglutide sets out the side effects to be aware of and explains how to report a suspected reaction via the Yellow Card scheme at yellowcard.mhra.gov.uk, a route available to patients as well as clinicians. If you're already on treatment with num and have a specific concern, our aftercare team is available seven days a week for exactly this kind of question. No appointment needed; it is part of what your prescription covers.

If you are considering starting treatment and want to talk through your cycle history and what to expect, checking your eligibility is a good first step.