What are Mounjaro side effects and how to overcome them

What are the side effects of Mounjaro? 

Listed most common first. 

Stomach and gut side effects peak while the dose is being increased, then ease as the body adapts to each new step. They are mostly mild: around three quarters were graded mild in the trials, and most of the rest were moderate (Mounjaro SmPC). 

Can Mounjaro cause low blood sugar if you are not diabetic? 

If you are taking Mounjaro injections for weight loss and do not have type 2 diabetes, low blood sugar is uncommon. The risk is real though if you also take insulin or a sulfonylurea such as gliclazide, and that needs managing. 

Mounjaro prompts insulin release only when blood glucose is already raised. At normal blood glucose it does very little. That is the reason it rarely causes a hypo on its own. 

Insulin and sulfonylureas such as gliclazide behave differently. They lower blood glucose whatever the starting level, so adding Mounjaro on top can take it too far down. Anyone on either drug may need their dose reduced first, though not on their own initiative. Speak to your prescriber about this. 

Recognising low blood sugar 

Shaking and sweating are usually the first signs, along with a racing heart, sudden hunger, dizziness, irritability, and difficulty holding a thought. Some people only notice it overnight or on waking. 

What to do if it happens 

• Take 15 to 20g of fast-acting sugar straight away: four or five glucose tablets, a small glass of fruit juice, or a regular (not diet) fizzy drink. 

• Wait 15 minutes and retest if you have a meter. Repeat if you are still low. 

• Once you’re feeling better, follow up with protein and a slower-release carb – hummus with oatcakes, or mixed nuts and seeds with a few berries. 

• Leave out chocolate and crisps. Fat slows sugar absorption, and speed is the whole point. 

Reducing the risk 

• Do not skip meals, even when your appetite has all but gone. Undereating accounts for a great deal of the unwellness people report on this medicine. 

• Eat something before exercise. 

• Drink alcohol in moderation and with food, never on an empty stomach. It can drop your blood sugar hours later, typically overnight. 

• If you take insulin or gliclazide, sort the dose out, by speaking with your GP or specialist, before you start Mounjaro, not after.  

How do I stop feeling sick on Mounjaro? 

Nausea affects more people than any other side effect, and for most it eases within a few weeks. What catches people out is when it comes back briefly after every dose increase. 

What helps: 

• Smaller meals, more often. A large plate is the single most reliable trigger there is. 

• Stop eating when you feel full rather than when the plate is empty. Your stomach is emptying more slowly than it used to. 

• Cut back on fatty, fried and rich food. That’s what sits heaviest. 

• Don’t lie down straight after eating. A short walk works better. 

• Sip water throughout the day instead of drinking a lot at meals. 

• In a bad week, plain and dry is better than interesting, have toast, crackers and rice. 

If it’s not settling, holding at your current dose for longer before stepping up is usually enough to fix it. Speak to us before changing anything yourself. 

Seek medical help the same day if you cannot keep fluids down, or if you develop severe abdominal pain that radiates through to your back. This can indicate pancreatitis, which is rare but serious. 

Why does Mounjaro cause constipation and diarrhoea? 

Both can happen and some people experience either of them at different points in the same course. Mounjaro slows the gut down, and most people on Mounjaro are eating less food, so there is less fibre and less bulk to move. 

Constipation: more fibre, more fluid, more walking. If that does not shift it, a pharmacist can suggest a laxative. 

Diarrhoea: keep your fluids up and stick to plain food for a few days. It usually settles by itself. If it does not or you become dizzy or are barely passing urine, seek immediate medical help. Dehydration on this medicine can affect the kidneys. 

Why am I bruising on Mounjaro? 

Small bruises where you inject are common, and how you are injecting Mounjaro is usually the reason. 

• Move the site every week: abdomen, thigh, back of the upper arm. Do not keep returning to the same spot. 

• Let the pen warm to room temperature. Cold solution stings, and stinging makes people flinch. 

• Do not rub afterwards. Press gently if you need to. 

• Inject at 90 degrees, depress the plunger slowly, and hold for a few seconds before withdrawing. 

• Steer clear of skin that is already bruised or scarred, and of the line where a waistband sits. 

Bruises appearing where you have not injected are another matter, and we would want to know. The same goes for bruising alongside bleeding gums or nosebleeds. We have a detailed guide about how to inject Mounjaro. 

Why am I so tired on Mounjaro? 

Usually this is diet, not drug. You are eating a great deal less than your body is used to, and often less protein than it needs. 

What can help is having protein at every meal, fluids kept up, and no cutting your calories further than the medicine already has. If the tiredness drags on past a few weeks, get your iron and B12 checked. Losing weight quickly pulls both down. 

Does Mounjaro cause hair loss? 

Some people notice thinning a few months in which is due to the speed of weight loss. 

Fast weight loss, plus a sharp drop in protein, can tip many follicles into a resting phase at once. The shedding follows a few months later, and it tends to show up in the shower or on the hairbrush. It passes and the hair grows back once weight and diet settle. 

Protein, healthy iron levels, and a sensible rate of loss are what help here.  Taking daily multivitamins can also help avoid malnutrition and support your overall health. Treatments licensed for male pattern baldness address an entirely different problem and will do nothing for this. 

Are Mounjaro side effects different in women? 

The side effects are the same. A few things apply only to women, and they matter. 

• Mounjaro can make the combined pill less reliable, particularly while the dose is going up and if you are vomiting. Use condoms as well for four weeks after starting, and for four weeks after every dose increase, or move to a method that is not swallowed. Ask one of our clinicians if you are unsure. 

• Do not take Mounjaro if you are pregnant, trying to conceive, or breastfeeding. 

• Periods often change during rapid weight loss. That is generally the weight loss talking, not the medicine. 

• Women with PCOS/ PMOS frequently start ovulating again as the weight comes off, so pregnancy can happen when it was not expected. 

How long do Mounjaro side effects last? 

The worst of the side effects happen in 2 – 4 weeks of starting treatment, and for about a week after each dose increase. 

Still struggling after a month at the same dose? That is not something to endure. Staying on a lower dose for longer usually sorts it, and it is no sign that the treatment has failed. 

When should I seek medical help? 

Seek urgent medical help if you experience: severe abdominal pain radiating to the back; persistent vomiting where you cannot keep fluids down; signs of a severe allergic reaction, such as swelling of the face or throat or difficulty breathing; or a lump or swelling in the neck, difficulty swallowing, or persistent hoarseness. 

For anything less urgent, please contact us. Side effects should also be reported through the MHRA Yellow Card scheme, which is how safety problems with medicines are spotted.