Many women taking GLP-1 receptor agonists such as semaglutide (Ozempic, Wegovy) or liraglutide (Victoza, Saxenda) wonder whether these medications might affect their menstrual cycle. Whilst GLP-1 medications do not directly alter reproductive hormones, the significant weight loss they facilitate can indirectly influence period regularity through well-established metabolic pathways. Understanding the relationship between weight loss, hormonal balance, and menstrual function is essential for women considering or currently using these treatments. This article examines the evidence, explores why periods may change during GLP-1 therapy, and clarifies when medical review is appropriate.

What Are GLP-1 Medications and How Do They Work?

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of medications originally developed for type 2 diabetes management, with some now also licensed for weight management. In the UK, semaglutide is available as Ozempic (for diabetes) and Wegovy (for weight management), while liraglutide is available as Victoza (for diabetes) and Saxenda (for weight management).

These medications work by mimicking a naturally occurring hormone called GLP-1, which is released by the intestines after eating. The mechanism of action includes several key effects:

• Stimulating insulin secretion from the pancreas in a glucose-dependent manner, helping to control blood sugar levels

• Slowing gastric emptying, which prolongs the feeling of fullness after meals

• Reducing appetite through effects on brain centres that regulate hunger

• Decreasing glucagon secretion, which helps prevent excessive glucose production by the liver

By targeting these multiple pathways, GLP-1 medications can lead to significant weight loss when combined with lifestyle modifications. The extent of weight loss varies by product—for example, semaglutide 2.4mg (Wegovy) has shown average weight loss of approximately 15% after 68 weeks in clinical trials, while liraglutide 3mg (Saxenda) typically achieves 5-8% weight loss.

There is no established direct pharmacological mechanism by which GLP-1 receptor agonists affect the menstrual cycle or reproductive hormones, and menstrual disorders are not listed as common adverse reactions in UK product information. However, the metabolic changes they produce—particularly significant weight loss—can indirectly influence menstrual regularity through well-established physiological pathways. Understanding this distinction is important when considering reports of period changes in women taking GLP-1 medications.

Why Weight Loss May Influence Period Regularity

Rapid or significant weight loss, regardless of the method used to achieve it, can affect menstrual cycle regularity through several interconnected mechanisms. This relationship is well documented in medical literature and applies to weight loss achieved through any means—diet, exercise, bariatric surgery, or medication.

Adipose tissue (body fat) plays an active role in hormone metabolism. Fat cells produce oestrogen through the conversion of androgens, and they also influence levels of sex hormone-binding globulin (SHBG), which affects the availability of reproductive hormones. When substantial weight loss occurs, these hormonal balances shift, potentially leading to temporary menstrual irregularities.

Key factors that may contribute to period changes during weight loss include:

• Reduced leptin levels: This hormone, produced by fat cells, signals energy availability to the brain. Rapid decreases can affect the hypothalamic-pituitary-ovarian axis

• Changes in body fat percentage: Particularly relevant when body fat drops below certain thresholds

• Caloric restriction effects: Even with adequate nutrition, significant energy deficits can temporarily suppress reproductive function

• Metabolic adaptation: The body may prioritise essential functions over reproduction during periods of rapid metabolic change

For women taking GLP-1 medications, the weight loss achieved may be more rapid than with lifestyle changes alone, potentially increasing the likelihood of temporary menstrual disruption. In some cases, significant weight loss and energy deficit can lead to functional hypothalamic amenorrhoea, where the brain temporarily reduces signals to the ovaries.

While some participants in clinical studies have reported menstrual changes, these are generally attributed to the metabolic effects of weight loss rather than direct drug action on reproductive tissues, and are not classified as common adverse effects in the UK product information for GLP-1 medications.

PCOS, GLP-1 Treatment and Menstrual Changes

Polycystic ovary syndrome (PCOS) affects approximately 10% of women of reproductive age in the UK and is characterised by irregular periods, elevated androgens, and often insulin resistance. Women with PCOS frequently experience oligomenorrhoea (infrequent periods) or amenorrhoea (absent periods), making this population particularly relevant when discussing GLP-1 medications and menstrual changes.

Interestingly, GLP-1 receptor agonists may actually improve menstrual regularity in women with PCOS, contrary to concerns about irregular periods. Research suggests several beneficial mechanisms:

• Improved insulin sensitivity: Insulin resistance is a key driver of PCOS symptoms, and GLP-1 medications can enhance insulin action

• Weight loss effects: Even modest weight reduction (5–10% of body weight) can restore ovulation and regular cycles in women with PCOS

• Reduced androgen levels: Weight loss and improved insulin sensitivity often lead to decreased testosterone and other androgens

• Restoration of ovulation: Some women with PCOS who previously had absent periods may begin ovulating regularly

NICE Clinical Knowledge Summary on PCOS recommends lifestyle modification and weight loss as first-line interventions for overweight women with the condition. Whilst GLP-1 medications are not currently licensed specifically for PCOS treatment in the UK, they may be prescribed for weight management or type 2 diabetes in women who also have PCOS.

An important consideration: Women with PCOS who have not been having regular periods may experience a return to fertility when starting GLP-1 treatment and losing weight. This means contraception becomes essential if pregnancy is not desired, as ovulation may resume unexpectedly. Additionally, GLP-1 medications are not recommended during pregnancy, and for semaglutide specifically, treatment should be discontinued at least 2 months before a planned pregnancy. Healthcare professionals should discuss these considerations with all women of reproductive age with PCOS who are starting these medications.

When to Speak to Your GP About Period Changes on GLP-1

Whilst some menstrual changes may be expected during significant weight loss, certain symptoms warrant medical review to rule out other causes and ensure appropriate management. It is important to distinguish between temporary, benign changes and those requiring investigation.

Contact your GP or healthcare provider if you experience:

• Complete absence of periods (amenorrhoea) for three months or more, particularly if you previously had regular cycles

• Very heavy bleeding requiring pad or tampon changes every hour, or passing large clots

• Bleeding between periods (intermenstrual bleeding) or after intercourse

• Severe pelvic pain accompanying menstrual changes

• Any possibility of pregnancy, especially if you have PCOS and were previously not ovulating regularly

Seek urgent medical attention if you have:

• Heavy bleeding that soaks through pads/tampons hourly for more than 2 hours

• Dizziness, fainting, or severe weakness with bleeding

• Severe abdominal pain with a positive pregnancy test

Your GP may recommend investigations depending on your symptoms and medical history. These might include:

• Pregnancy test: Essential first step for any woman of reproductive age with menstrual changes

• Blood tests: To assess hormone levels (FSH, LH, oestradiol, prolactin, thyroid function) and full blood count if bleeding is heavy

• STI screening: Particularly for unexplained intermenstrual or postcoital bleeding

• Pelvic ultrasound: If structural causes need to be excluded

• Review of medication: To ensure no drug interactions or other contributing factors

Keep a menstrual diary noting cycle length, flow heaviness, and any associated symptoms. This information helps your healthcare provider assess patterns and determine whether investigation is needed.

Regarding contraception, for most GLP-1 medications (semaglutide, liraglutide), there is no clinically significant effect on oral contraceptive effectiveness. However, if you experience vomiting or severe diarrhoea, follow the usual advice for missed pills. For tirzepatide specifically, non-oral contraception or additional contraceptive precautions are recommended for 4 weeks after starting treatment and after each dose increase.

Most menstrual irregularities associated with weight loss are temporary and resolve as your body adjusts to its new weight. However, professional assessment ensures that any changes are appropriately monitored and that other treatable causes are not overlooked.

If you experience any side effects you believe may be related to your medication, you can report them through the MHRA Yellow Card scheme.

Frequently Asked Questions