Mounjaro Mood Swings: What to Know (October 2026)

01 · The core answer

Can Mounjaro cause mood swings?

Mood swings are not a listed side effect of Mounjaro in the UK patient leaflet, so they are not an established effect of the medicine. It is also not something we can rule out for every individual. Anyone who feels different after starting treatment deserves to be taken seriously.¹¹³

Mounjaro is the brand name for tirzepatide, which works by activating the GIP and GLP-1 receptors to help regulate appetite and slow stomach emptying.¹ Those effects are on appetite and digestion.

Plenty of people ask the question because they feel more irritable, flat or tearful after a few weeks on treatment. That experience is real even where the cause is unclear. Several things change at once when you start: you eat differently, you have a new weekly routine, your dose steps up after at least 4 weeks on each dose, and your relationship with food may shift. Any of these can colour how you feel on a given day.

Regulators have looked 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. What matters in practice is simple: if your mood worsens, tell someone.

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.

02 · Your next step

What to do if your mood has changed

Speak to your prescriber or GP as soon as you notice a persistent change, and do not wait for your next scheduled review. Say when it began, how it relates to your injection day, whether you have changed dose recently and how your eating and sleep have been. That timeline helps them judge whether the medicine, your circumstances or something else is the most likely explanation.

Any change to your treatment should be agreed with a prescriber. Our prescribing team carries out ongoing monthly reviews and offers side-effect support, so you have a route to ask.

If you ever 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, or call Samaritans free on 116 123, day or night. That applies whatever medicine you take and whatever the cause.

You can also report any suspected side effect through the MHRA Yellow Card scheme, which helps regulators spot patterns that individual patients cannot see.¹⁹

03 · Deciding

Should mood concerns stop you starting treatment?

Not automatically, but they are worth raising before you start. Tell the prescriber about any history of low mood, anxiety, disordered eating or other mental health conditions on your consultation form. Mounjaro is a prescription-only medicine supplied only after an online consultation reviewed by a GPhC-registered prescriber, and that review is the place where this context is weighed.¹

You can also read related guides on whether Mounjaro can give you mood swings and on how Mounjaro and mood interact, which look at the same question from slightly different angles.

04 · What the label says

What the product information says about mood

The SmPC and the patient information leaflet are the two documents that set out the recognised side effects of Mounjaro, and mood swings are not listed as a side effect in either. That is a statement about what is established, not a claim that no individual has ever felt different on treatment.¹¹³

They list the side effects that are recognised, how serious they are and when to get medical help. If a symptom is not in them, that does not make it unimportant; it means it is not listed as a side effect in the UK patient leaflet.

Mounjaro is licensed in the UK for weight management in adults and for type 2 diabetes. It comes as a pre-filled multi-dose pen, the KwikPen, in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹

So how should you treat a symptom that is not on the label? Treat it as information worth sharing. Prescribers want to hear about new symptoms because that is how unexpected patterns come to light. Your report may be the first sign of a real signal, or it may point to something else that needs attention. Either way, the right move is to say so.

That is also the purpose of the Yellow Card scheme run by the MHRA. Anyone can submit a report about a suspected side effect, including patients themselves, and you do not need to be certain the medicine is responsible.¹⁹ Reports are reviewed collectively by the regulator. Social media posts cannot tell you whether the medicine, the diet change or an unrelated event caused a feeling.

If you want a plain summary of what to expect from the medicine, our guide to Mounjaro side effects and mood swings covers the same ground in a shorter form.

05 · Why mood may shift

Why your mood might feel different on treatment

Mood can feel different on Mounjaro for reasons that are indirect and personal, even though mood swings are not an established effect of the medicine. Understanding those reasons helps you describe what is happening to your prescriber, which is more useful than a general worry.¹

The first is eating. Tirzepatide activates GIP and GLP-1 receptors, which helps regulate appetite and slow how quickly the stomach empties. In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹ Eating noticeably less, or at different times, is a big change in a person's day. Some people find that mealtimes were a source of comfort or social connection, and that loss can feel unsettling.

The second is routine. A weekly injection is a new habit, and you may have started tracking food, weighing yourself or going to appointments. Some people find that motivating. Others find it stressful or tiring, especially in the first weeks.

The third is dose steps. Each step can bring a new adjustment period. If you notice your mood is worse around the days after a dose increase, write that down. It is a useful observation for your prescriber, although it does not prove the dose is the cause.

The fourth is the emotional side of weight change. Whether your progress is faster or slower than you hoped, the body changing is something people feel strongly about, and it is normal for feelings to go up and down.

None of this proves a cause for any one person. If a low mood is persistent, interferes with daily life or comes with other worrying symptoms, it needs assessing in its own right, not waiting out.

06 · Other causes of mood swings

Other causes of mood swings that are not Mounjaro

Mood swings have many common causes that have nothing to do with medication, and it is worth considering them before assuming the injection is responsible.

Everyday causes include poor sleep, stress at work or at home, bereavement, relationship strain, hormonal changes around periods, pregnancy, the perimenopause and the menopause, alcohol, caffeine and other medicines. A GP can arrange the right checks. None of these is specific to Mounjaro, and any of them can begin at the same time as treatment by coincidence. 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.

Is it normal to experience mood swings while losing weight? Many people do report feeling more emotional during a major lifestyle change. That is a general observation about change, not a finding we can attribute to any one method of losing weight. Dieting hard, cutting out foods you rely on, or feeling hungry or tired can affect temper and energy. If your mood is a problem, say so.

If you already have a diagnosis such as ADHD, bipolar disorder, depression or anxiety, tell your prescriber on your consultation. That judgement belongs to a clinician who can see your full history. The same applies if you take regular medication from a mental health team.

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. Working out the cause can wait; your safety cannot.

07 · Worst side effects

The worst side effects of Mounjaro and when to seek help

Like all medicines, Mounjaro can cause side effects, and most are digestive. The most common, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort.

Read the side-effects section of the patient leaflet before your first dose, not after a problem starts. Keep the leaflet somewhere you can find it. When something feels wrong, check whether the symptom is listed and what the leaflet advises. If a symptom is serious, get medical help straight away; for other new or lasting symptoms, tell your prescriber.

Digestive effects are the most common side effects, especially when starting or increasing a dose. 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 Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed. This applies to the pill only; implants, coils and injections are unaffected. If you take insulin or sulfonylureas, doses may need adjusting because of the risk of low blood sugar, so tell your prescriber.

A practical point: feeling physically unwell can itself change how you feel emotionally. Persistent sickness, poor sleep or exhaustion can make anyone short-tempered or low. If the physical symptoms are the real problem, addressing them with your prescriber may improve your mood too.

If you notice something that is not in the leaflet, including mood changes, you can still report it. The Yellow Card scheme accepts reports of any suspected side effect, and you do not need proof of cause.¹⁹ Our prescribing team also provides side-effect support to customers, so contact us if you are unsure what to do.

For a broader look at this class of medicine, see our guide on whether weight loss drugs cause mood swings.

08 · Improving your mood

How to improve mood on Mounjaro

The most useful step is to tell your prescriber how you feel, then look after the basics that influence mood for everyone. The tips here are general wellbeing habits, not medical advice. They do not replace an assessment.

Start with food. Mounjaro is used alongside a reduced-calorie diet and increased physical activity, and it is meant to support, not replace, those habits.¹ Eating regular, balanced meals, rather than skipping them because you are not hungry, helps many people feel steadier. If you are struggling to eat enough, say so to your prescriber, because that is a reason to review your plan.

Move in ways you enjoy. Increased physical activity is part of the treatment approach, and a walk outdoors is also a well-known way to clear the head. Choose something realistic, not punishing. Gentle consistency is more likely to last than an extreme plan.

Protect your sleep. Keep regular hours, limit screens late at night and keep caffeine and alcohol in check. Poor sleep makes almost everyone more irritable, and it is easy to blame the wrong thing.

Keep a simple diary. Note your injection day, dose, meals, sleep and mood each day. After a few weeks, patterns often show up, such as a dip on one particular day of the week or after a dose step. Bring that to your review. It turns a vague worry into something a clinician can work with.

Talk to people. Friends, family or a support group can help, and many people find the journey easier when it is shared. Our free GLPTrackr companion app helps you track your GLP-1 journey, which some people find useful for spotting patterns.

Do not change your treatment on your own. If you want to pause or stop, discuss it first. Our guide to GLP-1 medicines and mood adds more background.

09 · Expectations and stopping

Expectations, stopping treatment and how long it stays in your system

Realistic expectations protect your mood as much as anything, because disappointment with progress is a common source of low feelings. Mounjaro works alongside a reduced-calorie diet and increased physical activity, not instead of them. Results vary, and trial averages do not predict your own result.

At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight.

If you feel your mood is linked to treatment and want to stop, speak to your prescriber first. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

Stopping brings its own questions about appetite and weight, and a prescriber can help you plan. Mounjaro manages weight; it does not cure the biology behind it. In SURMOUNT-4, people who stopped tirzepatide after 36 weeks regained on average 14% of body weight over the following year, while those who continued treatment lost a further 5.5% on average. Stopping should always be planned with your prescriber, with diet and activity habits ready to carry the load. You do not have to decide alone, and you do not have to decide in a low moment.

Where does the NHS fit? 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 at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first (initially BMI 40+ with four or more qualifying conditions). Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.⁴⁵ Whichever route you take, a named clinician should be monitoring how you feel.

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

11 · Support from us

Support with EverydayMeds

Tell the prescriber about any mental health history in your free online consultation, which is reviewed by a GPhC-registered prescriber.

Aftercare includes ongoing monthly reviews, dose-titration and follow-up assessments by the prescribing team, plus side-effect support. Repeat orders re-check suitability, and there is no auto-shipping, so nothing arrives without you choosing it. If you feel your mood has changed, that review is the place to raise it. You can also reach support Monday to Friday, 9am to 5pm, at support@everydaymeds.co.uk, by phone on 0333 207 0413 or through the account portal chat.

Store your pen in the fridge at 2–8°C until first use. Once in use, a KwikPen can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use. Our guide to weight loss injections and mood swings and our page on whether Mounjaro can cause mood swings offer further reading. Mounjaro is a prescription-only medicine, used alongside a reduced-calorie diet and increased physical activity. Individual results vary, and this page is information, not a substitute for medical advice.