Women's Weight Loss Injections: How They Work and What to Expect

Do weight loss injections work differently for women than for men?

The short answer is: the licensed medicines are the same regardless of sex, but several factors that are more common in women's lives can shape how treatment goes in practice. Hormonal fluctuations across the menstrual cycle, perimenopause and menopause can affect appetite, fat distribution and metabolic rate, all things your prescriber takes into account when reviewing your health history.

Clinical trial data for both Mounjaro and Wegovy included large numbers of women, and results were broadly consistent across sexes. SURMOUNT-1, the pivotal tirzepatide trial, reported average body-weight reductions of around 20–21% at the highest dose over 72 weeks; the STEP 1 trial for semaglutide 2.4mg reported around 15% over 68 weeks. Both trials required participants to follow a reduced-calorie diet alongside treatment. You can read the full NICE appraisal of tirzepatide for more on how the evidence was assessed, NICE technology appraisal TA1026 sets out the eligibility criteria and the underlying data in plain terms.

Body composition also plays a role. Women tend to carry a higher proportion of body fat relative to lean mass, which can mean weight loss feels slower on the scales than for men losing a similar percentage of fat tissue. This is worth knowing upfront, and it is one reason the clinical journey matters as much as the starting prescription. If you want to understand more about how weight loss injections work before comparing the two medicines head-to-head, our guide to the best weight loss injections for women covers that ground in detail.

What should women know about contraception and HRT while using these injections?

A question our prescribers hear most weeks is whether the injection affects the contraceptive pill. The answer for tirzepatide (Mounjaro) is yes, temporarily: because the medicine slows gastric emptying, oral contraceptives may be absorbed less completely, particularly early in treatment. NHS England's guidance on weight management injections advises adding a non-oral contraceptive method (condoms, for example) for the first four weeks on tirzepatide and for four weeks after every dose increase. Current evidence does not show the same effect for semaglutide (Wegovy), but this is worth raising with your prescriber if you have any concerns.

For women on HRT, NHS England specifically advises considering transdermal forms of HRT (patches or gels applied to the skin) while on tirzepatide, for the same absorption reason. Oral HRT is not contraindicated, but the conversation with your prescribing clinician is important before you start. None of this means these medicines are unsuitable for women on HRT or hormonal contraception, it means the clinical picture needs to be complete before your prescription is written.

Pregnancy and breastfeeding are clear exceptions. Neither Mounjaro nor Wegovy is recommended during pregnancy, while breastfeeding, or if you are actively trying to conceive. If your circumstances change during treatment, stop the medicine and speak to your GP without delay.

Who can get a prescription, and what does the process involve?

UK licensing covers adults with a BMI of 30 or above, or a BMI of 27 or above where a weight-related condition (type 2 diabetes, hypertension, obstructive sleep apnoea, high cholesterol) is also present. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance, so the numbers are not the whole story. The prescriber looks at the full picture: your medical history, current medicines (including the contraceptive and HRT points above), any contraindications, and your goals.

At nume, every consultation is read by a GPhC-registered Independent Prescriber, a real clinician who reviews your answers the same day, not software running a decision tree. You will also go through photo-ID verification and live weight confirmation on video, and your GP is notified in line with GPhC guidance. There are no subscriptions; every repeat order is clinically reviewed again before anything is dispensed. For a broader look at how the process works from the start, our overview of weight loss injections walks through each stage.

If you are curious about how costs are structured (what is and is not included in a quoted price) our weight loss injections prices page sets that out honestly, including what a transparent price should cover beyond the medicine itself.

What side effects are most common, and when should you get medical help?

Both medicines share a similar profile: nausea is the most frequently reported effect, followed by loose stools or constipation, indigestion, reduced appetite, fatigue and occasional headache. These effects are linked to the medicines slowing digestion, which is also part of how they reduce hunger. For most people they are mild to moderate and settle within the first few weeks of a new dose, and our page on the 3 weight loss injections available explains how the dosing schedule works for each one. Staying well-hydrated and eating smaller, lower-fat meals during the early weeks tends to help.

There are situations that need prompt medical attention. Severe stomach pain that spreads to the back (with or without vomiting) can be a sign of acute pancreatitis, which the MHRA flagged as a known but infrequent risk in its January 2026 drug safety update; call 999 or go to A&E rather than waiting. Signs of a serious allergic reaction (swelling of the face or throat, difficulty breathing) also need emergency care. Gallbladder problems are another known risk worth knowing about: right-sided pain under the ribs, particularly after eating, is worth reporting to your GP or prescriber promptly.

Suspected side effects from any medicine can be reported through the MHRA Yellow Card scheme. Doing so helps regulators build a clearer picture of real-world safety, and it takes about five minutes. Our FAQs page addresses some of the most common concerns people raise before and during treatment. If you have a specific question, our team is available seven days a week.

When you are ready to explore whether treatment is right for you, if you are a man looking at your options you can find out more through our guide to men's weight loss injections, or speak to our prescribers through a free consultation and get a same-day clinical review of your circumstances.