Brain Health and Weight Loss Injections: What We Know (October 2026)

01 · The honest answer

What can we say about brain health and weight loss injections?

Tirzepatide activates GIP and GLP-1 receptors, which help regulate appetite, slow how quickly the stomach empties and improve the body's response to insulin. Most people feel fuller sooner and less hungry between meals.¹

Read our guide to weight loss drugs and mental health for the wider picture.

02 · Mood

Do weight loss injections affect mental health?

Some people have asked whether these medicines affect mood. The EMA's safety committee reviewed the evidence on GLP-1 medicines and low mood or suicidal thoughts and concluded in 2024 that it does not support a causal link, and the MHRA keeps this under continuous review.¹⁷ That said, any big change in weight, appetite and routine can affect how you feel, so seek help promptly if your mood drops or you have distressing thoughts during treatment. If you have a history of low mood or anxiety, tell the prescriber during your free consultation so they can weigh it up.

If you have thoughts of harming yourself or ending your life, get help straight away. Call 999 or go to A&E if you are in immediate danger. In England you can call NHS 111 and choose the mental health option, any time. You can also call Samaritans free on 116 123, day or night. Tell your prescriber about any change in your mood while taking Mounjaro.

If you notice new or worsening symptoms once treatment has started, contact your prescriber and report them through the Yellow Card scheme.¹⁹ Our pages on whether Mounjaro affects mental health, whether it helps and mental health side effects go deeper.

03 · Next step

How do I get Mounjaro safely?

Mounjaro is licensed for adults with a BMI of 30 or above, or 27 to 30 with a weight-related condition, alongside a reduced-calorie diet and more activity.¹

Start your free consultation or see how to register online.

04 · Side effects early on

Early effects to expect

The first weeks on 2.5mg are about adjustment. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹ Digestive effects are covered in our gut health guide, and the body-wide angle in our cellular health article.

05 · Reproductive and other health

Menstrual, prostate and reproductive health

One point is established: the medicine can reduce absorption of oral contraceptives because stomach emptying slows.⁷ Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. If you become pregnant during treatment, stop the medicine and tell your prescriber promptly. The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ Discuss contraception and any reproductive health concern with your prescriber before starting.

06 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

07 · NHS access

NHS access to weight loss jabs

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus a weight-related condition, and the primary-care rollout began in June 2025 with the highest-need groups first, initially BMI 40+ with four or more qualifying conditions.⁴⁶ Many people who meet the licensed criteria choose regulated private treatment rather than wait. Compare options in all weight loss treatments or the weight loss injections hub.