Starting weight-loss injections? What women need to know about contraception and HRT

Weight-loss injections, contraception and HRT

Weight-loss injections such as Mounjaro® (tirzepatide) and Wegovy® (semaglutide) belong to a group of medicines called GLP-1 receptor agonists.

These medications help with weight loss by reducing appetite, improving blood sugar control and slowing the emptying of the stomach. While this helps you feel fuller for longer, it can also affect how some oral medications are absorbed.

For women, the main medicines we review alongside GLP-1 treatment are:

  • The contraceptive pill

  • Hormone Replacement Therapy (HRT)

GLP-1 medications and contraception

Current guidance from the Faculty of Sexual & Reproductive Healthcare (FSRH) advises that anyone who could become pregnant should use reliable contraception while taking GLP-1 medications, as there is limited safety data in pregnancy.

If you take the contraceptive pill, the effect on contraception depends on the specific medication.

Tirzepatide (Mounjaro®)

Tirzepatide is currently the only GLP-1 medication shown to reduce the effectiveness of oral contraception. If you use the combined pill or progestogen-only pill, guidance recommends that you:

  • Use condoms for four weeks after starting tirzepatide

  • Use condoms for four weeks after each dose increase

  • Alternatively consider switching to a non-oral contraceptive method during treatment 

Other GLP-1 medications

For other GLP-1 medicines, including semaglutide (Wegovy® or Ozempic®), there is currently no evidence that they reduce the effectiveness of the pill. Please be mindful, if you change from one of these to Mounjaro, the above advice will be relevant to you. 

However, these medications commonly cause nausea, vomiting or diarrhoea, particularly when starting treatment or increasing the dose.

If vomiting occurs soon after taking the pill, or if severe diarrhoea continues for more than 24 hours, you should follow standard missed-pill guidance, as absorption may be reduced.

Contraception methods that are not affected

GLP-1 medications do not affect contraceptives that are not taken orally, including:

  • coils (IUD or hormonal coil)

  • implants

  • injections

  • patches

  • vaginal rings 

These remain reliable options while using GLP-1 treatments.

GLP-1 medications and HRT

GLP-1 medications can affect how well oral HRT tablets are absorbed. The hormone we are particularly careful about is progesterone, which protects the lining of the womb (endometrium) when oestrogen is used as part of HRT.

If progesterone is not absorbed adequately, the womb lining may build up. This can increase the risk of:

  • unexpected bleeding

  • heavy bleeding

  • endometrial thickening

For this reason, women using GLP-1 medications may benefit from non-oral HRT options

Alternatives that may be recommended and we may discuss options such as:

Transdermal oestrogen - Oestrogen delivered through the skin, such as:

  • patches

  • gels

  • sprays

These bypass the digestive system and are not affected by delayed stomach emptying.

Non-oral progesterone

Many women choose a Mirena® coil, which releases progesterone directly in the womb and provides consistent protection of the endometrium.

Temporary progesterone adjustment

If oral progesterone is continued, a temporary dose adjustment may sometimes be recommended when starting or increasing GLP-1 medication.

Symptoms you should report

If you are taking HRT and a GLP-1 medication, please contact us if you experience:

  • bleeding after months or years without a period

  • spotting between periods

  • pelvic discomfort or bloating

  • unusual discharge or pelvic pain

These symptoms should always be assessed.

When to speak to a doctor

If you are using:

  • the contraceptive pill, or

  • oral HRT; 

and you are starting or currently using a GLP-1 weight-loss medication, it is sensible to review your treatment.

Our doctors can help make sure your contraception and HRT remain safe and effective while you are on treatment.

Sources:

FSRH (The Faculty of Sexual & Reproductive Healthcare): Patient Information GLP-1 agonists and contraception - published February 2025

Primary Care Women’s Health Society. Guidance for healthcare professionals - published April 2025

Catherine EldridgeComment