Mounjaro side effects: what to expect (and what you can do)

What is Mounjaro and how does it work?

Mounjaro is the brand name of tirzepatide, an injection you give once a week. The medicine mimics two gut hormones that your body makes itself (GLP-1 and GIP). These hormones send your brain a satiety signal and slow gastric emptying. You notice the result mainly in your head and your stomach: less hunger, feeling full sooner and fewer thoughts about food. Read more about the Mounjaro diet.

That is also exactly where the explanation for the side effects lies. Because Mounjaro slows your digestion, your gastrointestinal tract reacts most strongly: nausea, diarrhoea or, on the contrary, constipation. So the effect and the side effects come from the same source. That is also a reassuring thought: your stomach "noticing something" usually doesn't mean that something is going wrong, but that the medicine is doing what it was made for.

In terms of effect, for most users the feeling of hunger already decreases in the first weeks, and the weight follows after that. Expect a first visible effect after about 4 weeks. So losing weight with this medicine is not a sprint, and that is exactly why a calm, supervised build-up is more important than getting to a high dose as quickly as possible.

According to the European Medicines Agency (EMA), Mounjaro is approved for the treatment of type 2 diabetes and for weight management in obesity or overweight with weight-related health problems, always in combination with diet and exercise. In the Netherlands it is available on prescription only. Never buy Mounjaro without a prescription online: then you don't know what you're injecting and no doctor is keeping an eye on you. The safe route always goes through a doctor, as with supervised medical weight loss with injections.

The most common side effects of Mounjaro

By far most complaints are in the gastrointestinal area. These are the side effects users report most often:

• Nausea, sometimes with vomiting
• Diarrhoea or, on the contrary, constipation
• Reduced appetite, partly the intended effect of the medicine
• Abdominal pain, a bloated feeling, burping and heartburn
• Fatigue and feeling listless
• Headache and dizziness
• Redness or itching at the injection site
• Hair loss, usually temporary and linked to rapid weight loss

Important to know: reduced appetite is not a warning sign but the core of how it works. Above all, the medicine takes away the feeling of hunger. It only becomes a problem if you eat so little that you lack nutrients or feel listless. That's why responsible use always includes medical supervision and attention to what you do eat.

We get a lot of questions about that fatigue, and rightly so: "Mounjaro side effects fatigue" is one of the most searched combinations. The tiredness usually has two causes at the same time. The medicine itself can make you feel listless in the first weeks, and on top of that you're simply eating fewer calories, so your body needs to adjust for a while. For most users this improves after the adjustment phase. If the fatigue persists for weeks or gets worse, that is a signal to go through your eating pattern and your dose with a doctor.

How often does each side effect occur?

Not every side effect is equally likely. This table combines the frequencies from the official patient information leaflet with what you can do about them yourself. You'll find the full frequency classification on apotheek.nl, the medicines information of the pharmacists' organisation KNMP (the Royal Dutch Pharmacists Association).

Do you use Mounjaro alongside diabetes medication such as insulin? Then there is an extra risk of low blood sugar (a hypo). For people who use the medicine only for weight loss, that risk hardly plays a role.

Above all, read the table as reassurance with your eyes open. The chance that you'll notice something in the first weeks is real; the chance of a serious side effect is small. And note: "more than 1 in 10" also means that a large proportion of users have no complaints at all. You only know how your body reacts once you start, and that is exactly why a doctor who keeps an eye on you is not a luxury but a requirement.

Side effects per phase: start, dose increase and long term

The first weeks are the hardest. Your body has to get used to slower digestion, and you notice that mainly in weeks one to four. Nausea and a full feeling are the most commonly reported complaints in this phase. For most users they clearly subside after that.

Every dose increase can temporarily bring complaints back. Mounjaro is built up step by step, precisely to keep side effects limited. After each increase, your body may need a short adjustment period again. If an increase goes too fast for your body, a doctor can keep you on a lower dose for longer. You can read more about this in our article on Mounjaro dosage.

More and more is known about the long term. In the SURMOUNT-1 trial, a placebo-controlled study of 2,539 participants with obesity, users were followed for 72 weeks. Most side effects were mild to moderate and mainly occurred while the dose was being built up. Of the participants, 4% to 7% stopped because of side effects, compared with almost 3% in the placebo group. In other words: more than 9 in 10 participants were able to keep using the medicine for a year and a half.

For completeness: tirzepatide is a relatively new medicine, and effects over many years have not yet been fully mapped out. That's why it is under additional monitoring by the medicines authorities. If you experience a side effect, you can report it (in addition to discussing it with your doctor) to Bijwerkingencentrum Lareb, the Dutch reporting centre for side effects. This way, knowledge about the medicine grows for everyone who uses it.

What can you do yourself about side effects?

With a few adjustments to your eating pattern, you can prevent or ease most gastrointestinal complaints. These are the tips that help most in practice:

1. Eat smaller portions, spread over the day. Your stomach empties more slowly, so large meals literally sit heavily on your stomach.
2. Choose protein-rich food. You're eating less, so every bite counts. Enough protein also protects your muscle mass while you lose weight.
3. Drink 1.5 to 2 litres a day. That helps against constipation, headache and dizziness, and protects your kidneys with diarrhoea or vomiting.
4. Limit fatty, spicy and fried food. These are the best-known triggers for nausea.
5. Eat slowly and stop when you feel full. The full signal comes sooner than you're used to; eating past it increases the risk of nausea.
6. Be cautious with alcohol. Alcohol irritates the stomach and provides empty calories that slow your progress.
7. Rotate your injection site. This reduces the risk of skin reactions.

If your complaints persist despite these adjustments, it's not a matter of gritting your teeth. A doctor can slow down the dosing schedule, lower the dose temporarily or look with you at whether this medicine really suits you. So with side effects there is always a middle way between "pushing on" and "stopping", as long as someone who knows the options is keeping an eye on things.

Want to lose weight with medication, but with a doctor who keeps an eye on you when your body protests? At Qlinic you're supervised by our regular BIG-registered doctor (the BIG register is the Dutch register of healthcare professionals), with a personal check-up every 4 weeks. Take the eligibility check →

Is Mounjaro bad for your kidneys?

No, there is no evidence that Mounjaro directly damages your kidneys. The risk to the kidneys is indirect: with severe diarrhoea or persistent vomiting you can lose so much fluid that you become dehydrated, and dehydration can temporarily worsen kidney function. That risk is greatest in people who already have reduced kidney function.

In practical terms, this means two things. Drink enough, especially on days with gastrointestinal complaints. And keep an eye on your complaints: if vomiting or diarrhoea means you can't keep fluids down, contact your doctor. Existing kidney problems should be discussed at the medical intake in any case, so the doctor can assess beforehand whether the medicine is suitable for you.

That this question is asked so often is probably due to reports about similar medicines and the leaflet warning about dehydration. The answer remains nuanced: for healthy kidneys there is no proven direct risk, but preventing dehydration is always the rule with these medicines.

When should you contact a doctor?

Most side effects are unpleasant but harmless. A small number of signals do need immediate medical attention. Contact a doctor straight away if you have:

• Severe, persistent abdominal pain, sometimes radiating to your back, with or without vomiting: this may indicate pancreatitis
• Severe pain in the upper right of your abdomen, possibly with fever or yellowing skin: possibly gallstones or inflammation of the gallbladder
• Swelling of the face, lips, tongue or throat and difficulty breathing: a serious allergic reaction, stop straight away and call a doctor
• Persistent vomiting or diarrhoea that means you can barely keep fluids down
• Hypo symptoms (trembling, sweating, palpitations) if you also use diabetes medication

This is exactly why we believe weight loss medication should never be a DIY product. With medical weight loss with injections through Qlinic you have one fixed point of contact: our regular BIG-registered doctor, who speaks to you personally every 4 weeks. If you're unsure about something, you discuss it at the next check-up or sooner in consultation with the doctor. And if it still doesn't feel right, you look together with the doctor at whether pausing or stopping is sensible.

That fixed point of contact is the core of how we work: small-scale, with around 50 clients helped so far and a 5.0 on Google based on more than 20 reviews. Especially with questions about side effects, that makes a difference.

Mounjaro side effects during menopause

For women going through menopause, the side effects of Mounjaro are not different or worse, but the context is. Many women find that losing weight becomes harder from menopause onwards: hormonal changes, loss of muscle mass and a slower metabolism work against them. In this group in particular, medication that takes away the feeling of hunger can make the difference, as we explain in our article on weight loss during menopause.

There is one point of attention, though: menopause symptoms and side effects can resemble each other. Fatigue, palpitations, dizziness and mood swings occur with both. That can make it hard to tell what is caused by menopause and what by the medicine. A doctor who knows your situation and speaks to you every 4 weeks can make that distinction together with you and adjust the treatment accordingly. So always report these kinds of complaints at your check-up, even if you think it's "just menopause".

Two practical tips carry extra weight in this stage of life. Eat plenty of protein and keep using your muscles, because muscle mass is already lost faster during menopause and rapid weight loss reinforces that. And go easy on yourself in the adjustment weeks: the fact that your body needs to adjust for a while says nothing about whether the treatment will succeed.

Does this sound familiar: you've tried everything, but the kilos won't budge? Our doctor assesses whether medical weight loss with supervision suits your situation. Take the eligibility check →

Frequently asked questions about Mounjaro side effects

What are the downsides of Mounjaro?

The main downsides are the gastrointestinal side effects in the initial phase, the weekly injection and the costs, because in the Netherlands the medicine is usually not reimbursed for weight loss. In addition, the feeling of hunger often returns after stopping, so lasting results depend on supervision and an adjusted lifestyle.

How long can you use Mounjaro?

There is no fixed maximum duration of use; the doctor decides per person how long use is useful and safe. In research, tirzepatide has been used and monitored continuously for more than a year and a half. As long as the medicine works, is well tolerated and there is medical monitoring, the treatment can continue. Always evaluate the duration together with your doctor.

What can you eat on Mounjaro?

In principle you can eat anything, but you'll feel best with small, protein-rich meals that are low in fat and contain enough fibre. Also drink 1.5 to 2 litres a day. Fatty, spicy and fried food and alcohol increase the risk of nausea and are best limited.

Can Mounjaro cause eye problems?

In people who use Mounjaro only for weight loss, eye problems are not a known common side effect. The warning about eyes mainly applies to people with diabetes: a rapidly falling blood sugar can temporarily worsen an existing diabetic eye condition (retinopathy). If you have diabetes and notice a change in your vision, contact your doctor.

Does Mounjaro cause muscle pain?

Muscle pain is not listed among the common side effects in the patient information leaflet. What does play a role: with rapid weight loss you lose muscle mass as well as fat, which can cause weakness or a sensitive body. Eating protein-rich food and strength training limit that loss. If you have unexplained or severe muscle complaints, discuss them with your doctor.

Can Mounjaro cause itching?

Yes, itching occurs, usually as redness and itching around the injection site, in 1 to 10 in 100 users. This usually disappears by itself; rotating your injection site helps. If you get itching or a rash all over your body, or swelling of the face or throat, that may be an allergic reaction and you should contact a doctor straight away.

Why am I so tired on Mounjaro?

Fatigue from Mounjaro is usually caused by the combination of the medicine itself and the fact that you're taking in considerably fewer calories. For most users, the tiredness decreases after the first weeks. If it persists, look at your eating pattern (especially protein) and the pace at which the dose is built up together with your doctor.

Can Mounjaro cause palpitations?

Yes, an increased heart rate occurs in 1 to 10 in 100 users and is usually harmless. Persistent or severe palpitations, especially in combination with dizziness or chest pain, are a reason to contact a doctor straight away.

Can you just stop taking Mounjaro?

Medically speaking, you can stop whenever you want; you don't need to taper off to prevent withdrawal symptoms. Do bear in mind that the feeling of hunger returns and, without a plan, the weight often goes up again. So always stop in consultation with your doctor.

Are the side effects of Mounjaro different from those of Ozempic?

Largely not: both medicines mainly cause gastrointestinal complaints such as nausea, diarrhoea and constipation, because they both act on the GLP-1 system. Mounjaro (tirzepatide) also acts on a second hormone (GIP). You'll find a full overview per medicine in our articles on GLP-1 side effects and the comparison Mounjaro vs Ozempic.