Can Mounjaro Cause Mood Swings? (October 2026)

01 · The core answer

Does Mounjaro cause mood swings?

Mounjaro does not have an established direct effect on mood. Regulators have looked at this question specifically: the EMA's safety committee reviewed the evidence and concluded in 2024 that it does not support a causal link, and the MHRA keeps this under continuous review.¹⁷ Mood swings are not on the UK patient leaflet's list of side effects for Mounjaro, which are overwhelmingly digestive.¹

That is not the same as saying nobody feels different. Any big change in weight, appetite and routine can affect how you feel, so it is sensible to tell your prescriber about any history of depression and to seek help promptly if your mood drops or you have distressing thoughts during treatment.¹⁷

Our page on GLP-1 medicines and mood looks at the wider drug class.

02 · Your situation

Is this relevant to me?

It is relevant if you feel noticeably different since starting Mounjaro or since a dose increase, and especially if the change lines up with the days after your injection. That timing matters, because side effects follow a pattern: they appear in the first days after starting or increasing a dose, peak early and settle as your body adapts.¹

Ask yourself three questions:

• When did it start? Note whether it began after starting Mounjaro or after a dose increase, and tell your prescriber.
• Is it linked to eating or sleeping less? Feeling flat or short-tempered is understandable when you are tired, hungry or unwell.
• Is it severe, persistent or frightening? If so, do not wait for it to pass. Speak to your prescriber or GP.

03 · Next steps

What should I do next?

Start by telling your clinical team what you are noticing and when it began. They can review your dose, hold you on the current strength for longer before stepping up, and check whether something treatable is behind it. If a new dose is hard to tolerate, prescribers can hold the current dose longer before stepping up, and you should speak to your clinical team rather than pushing through severe symptoms.¹

Do not stop or adjust the medicine on your own. 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.

04 · What regulators found

What the regulators have concluded about mood

The most reliable answer to this question comes from safety regulators, not from online forums. Regulators have looked specifically at whether GLP-1 medicines are linked to low mood or suicidal thoughts: the EMA's safety committee reviewed the evidence and concluded in 2024 that it does not support a causal link, and the MHRA keeps this under continuous review.¹⁷

Two things are worth drawing out. First, "no causal link" is a conclusion about the evidence reviewed, not a promise about every individual. Second, continuous review means the question stays open to new data rather than being closed for good.

If you notice a new symptom that you think may be linked to the medicine, you can report it yourself through the MHRA Yellow Card scheme as well as telling your prescriber.¹⁹ Reports like this are how regulators spot patterns early. Our related page on whether Mounjaro can give you mood swings approaches the same question from the patient's angle.

05 · Indirect causes of mood changes

Why you might feel low or irritable on Mounjaro

Even without a direct drug effect on mood, several well-recognised parts of treatment can change how you feel.

Digestive side effects. The most common side effects are nausea, diarrhoea, vomiting, constipation and abdominal discomfort.¹ Feeling sick or uncomfortable for days is wearing for anyone, and it is easy to become short-tempered, withdrawn or tearful when your stomach is unsettled.

Tiredness. Fatigue is a recognised common side effect, most noticeable in the first weeks and after dose increases. It usually reflects a mix of the body adjusting and simply eating less.¹ Low energy lowers patience and motivation, which can look like a mood change.

Dizziness and reduced appetite. Both are listed as common effects.¹ Skipping meals or feeling lightheaded can leave you feeling edgy, particularly if you are not drinking enough.

Big changes in routine. Eating less, rethinking food, changing your relationship with meals out and social eating, and watching your body change are all adjustments. Regulators note that any big change in weight, appetite and routine can affect how you feel.¹⁷

Low blood sugar, if you take certain diabetes medicines. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion), because your prescriber may need to adjust those medicines.¹ Treat this as a medical issue rather than a mood issue and speak to your prescriber.

06 · Timing and dose increases

Timing: when mood changes are most likely

If anything is going to feel different, the first weeks and the days after each dose increase are the most likely window. Most side effects appear in the first days after starting or increasing a dose, peak early and settle as your body adapts, and for most people they ease within days to a few weeks as the body adjusts.¹

This is one reason Mounjaro uses a gradual dose ladder.

A useful habit is to keep a short note each week: the day you injected, how you slept, what you ate and how you felt. Patterns show up quickly. If the low or irritable days cluster in the days after each injection, your prescriber can use the note to decide whether to hold your dose. Our free companion app, GLPTrackr, is available on iOS and Android if you want somewhere to keep it.

If your mood stays low well beyond the early weeks, or gets worse rather than better, do not assume it is just adjustment. Raise it with your prescriber.

07 · What helps in practice

How to improve mood on Mounjaro

Practical steps can ease the side effects that make treatment harder going. None of these replaces advice from your own clinical team.

Settle your stomach. Eat smaller meals slowly, stop at the first feeling of fullness, favour plain lower-fat foods while adjusting, stay well hydrated, and avoid lying down straight after eating.¹ If nausea or vomiting is persistent or you cannot keep fluids down, contact your clinical team — dehydration needs prompt attention.¹

Protect your energy. Keep meals balanced (protein especially), stay hydrated, and keep gentle activity going. Tell your clinical team if tiredness is severe or not settling.¹

Deal with constipation early. Fluid first, then fibre from vegetables and whole grains, plus daily movement. A pharmacist can recommend a suitable laxative if it persists.¹ Feeling bloated and blocked does nothing for your temper.

Look after the basics. Regular sleep, daylight, time outdoors and contact with friends and family are sensible for anyone adjusting to a major change, and they cost nothing.

Ask for a slower pace. If a dose step is hard to tolerate, your prescriber can hold the current dose longer before stepping up.¹ Slowing down is a normal clinical option, not a failure.

Talk to someone. If low mood or anxiety is part of your picture, your GP can offer support that is entirely separate from your weight treatment. You do not have to choose between the two.

08 · When to get help

When to seek help for your mood

Seek help promptly if your mood drops or you have distressing thoughts during treatment.¹⁷ You do not need to work out whether Mounjaro is responsible before you ask. That is the job of your prescriber and GP.

Tell your GP or prescriber if your mood drops or you have distressing thoughts during treatment.

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.

Separate from mood, some symptoms need medical help straight away for physical reasons: severe, persistent stomach pain that may spread to your back, pain in the upper right abdomen with fever or yellowing of the skin or eyes, or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing.¹

You can also report any suspected side effect through the Yellow Card scheme.¹⁹

09 · Weight loss drugs and mood

Is this specific to Mounjaro?

Many people ask the same thing about other treatments, and we cover those angles separately: see whether weight loss drugs cause mood swings and whether weight loss injections can cause mood swings.

For wider reading on specific symptoms people report, our guides to Mounjaro side effects and mood swings and Mounjaro's effects on mood take a closer look.

10 · 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