If you’re thinking about taking Mounjaro, you probably have many questions, not least how to weigh up the benefits against the possible side effects. Mounjaro is an exciting new treatment for weight management (and type 2 diabetes). But like any medication, it does come with possible side effects.
The good news is most users find that the side effects are mild, short-lived and manageable. In one study, only 8.5% of people on a 10mg or 15mg dose stopped taking the drug because of side effects. That means more than nine in 10 users wished to continue, despite any issues they may have encountered.
Dealing with side effects, if you’re unlucky enough to experience them, can be disheartening. But information is power here. The better you understand what may await you, the better placed you’ll be to navigate the journey ahead.
How does Mounjaro work?
Before we drill down into the possible side effects, here’s a quick primer on how Mounjaro works for weight loss. The active ingredient (a molecule called tirzepatide) is known as a ‘dual GIP-GLP-1 receptor agonist’, which means it mimics two hormones called GIP and GLP-1. These hormones are produced by the intestines during a meal, stimulating the release of insulin and helping to control blood sugar levels. That is why Mounjaro works so well for managing type 2 diabetes.
Mounjaro also has a clever double mechanism that contributes to weight loss. Through copying the effects of GLP-1, it slows down the transit of food through the stomach, helps you feel fuller faster and reduces cravings. And through copying the effects of GIP, it helps regulate energy balance.
Studies have found that this double mechanism—as a GLP-1 and GIP receptor agonist—is better for blood sugar control, insulin sensitivity, fat metabolism and weight loss than treatment with GLP-1 agonists taken alone.
Does everyone get side effects from Mounjaro?
Unfortunately, it’s impossible to say beforehand how your body will respond to Mounjaro. Some people experience no side effects, while others develop mild ones. And a far smaller proportion deal with something more severe. Everyone’s different, and your friend’s experience of Mounjaro may not reflect your own.
That’s why doctors will always start you on a low dose—to prevent side effects and allow your body to slowly adjust to the medication. The dose may be increased by 2.5mg every month depending on your individual needs and preferences.
The good news is that side effects could be temporary, and might ease off as your body gets used to the drug.
What are the most common side effects of Mounjaro?
Among those who do experience side effects, the most commonly reported are as follows:
- A general sense of weakness
- Burping and flatulence
- Constipation
- Diarrhoea
- Dizziness
- Gastrointestinal discomfort
- Hair loss
- Low blood pressure
- Lethargy
- Feelings of malaise
- Nausea
- Vomiting
- Injection site reactions like irritation, itching and bruising.
So how common are some of these issues, and what might be behind them?
Gastrointestinal symptoms
Let’s start with those pesky gut troubles. One study found that 19.2% of Mounjaro users experienced nausea, 16.4% experienced diarrhoea, 8.5% experienced vomiting, 4.5% suffered constipation and 4.5% abdominal pain. That’s because Mounjaro slows down the movement of food through your digestive system, which can lead to gastrointestinal discomfort.
Mood changes
Some people taking Mounjaro have reported mental health side effects, such as feelings of irritability or agitation.
Luckily, more serious mood changes are very rare. The US FDA has been investigating whether weight loss drugs might be linked to suicidal thoughts or actions. But it has not found any association to date.
Dizziness and low blood pressure
In studies, Mounjaro has been shown to lower patients’ blood pressure. Mounjaro could induce long-term effects on blood pressure as weight loss progresses (which is definitely an added bonus for people with hypertension). But a small number of people experience acute low blood pressure episodes that can cause dizziness. And as Mounjaro can suppress thirst signals, some people might drink less fluids, which can also give rise to dizziness. That’s why it’s so important to ensure you’re drinking enough water if you’ve been prescribed Mounjaro.
Weakness and lethargy
Some people have also reported tiredness, weakness and lethargy when taking Mounjaro. This could be associated with low blood sugar (more common in patients already taking medications for diabetes), or could be due to being at a calorie deficit. Feeling this way isn’t super common though—in one clinical trial, only 2.6% of Mounjaro users said they suffered from fatigue.
Hair loss
Although it might not fit with your dream post-Mounjaro aesthetic, 4% of users have reported alopecia (hair loss). This is probably due to the effects of weight loss or nutrient deficiency, which can sometimes spark a condition called telogen effluvium. That happens when more hairs than usual move into the shedding phase at the same time. Speak to your clinician if this is something you experience.
What are the more serious side effects of Mounjaro?
There are also a few more serious side effects to be aware of, including:
- Gallbladder disorders
- Very low blood sugar
- Pancreatitis
- Kidney disease
- Thyroid cancer
- Allergic reactions
- Diabetic retinopathy
While these problems are unlikely to happen, it’s really important that you can pick up on any issues that might warrant medical attention. Let’s run through them one by one:
Gallbladder disorders
If you have any pre-existing gallbladder problems, Mounjaro probably won’t be prescribed to you. In clinical trials, 0.6% of patients developed an acute gallbladder disorder (such as inflammation of the gallbladder or gallstones). If you develop a high fever, yellowing of the skin, or a sudden pain in the right upper part of your abdomen or between your shoulder blades, seek medical help right away.
Very low blood sugar (hypoglycemia)
When blood sugar levels drop below the normal range, you may experience dizziness, anxiety, sweating, shaking, and confusion. In clinical trials, mild hypoglycemia was relatively common, but severe hypoglycemia was very rare. It becomes more likely, though, if you’re also taking other diabetes medications like insulin or sulfonylureas. Talk to your doctor if that applies.
Pancreatitis
Very rarely Mounjaro users can develop acute pancreatitis, a condition in which the pancreas becomes inflamed. The symptoms include severe pain in your abdomen and a high fever. It can sometimes become a chronic problem. If you experience these symptoms, seek medical attention immediately. If you have a previous history of pancreatitis, you should not take Mounjaro.
Kidney problems
A few patients taking Mounjaro have developed acute kidney injury, mostly after severe episodes of vomiting and diarrhoea. If you experience these symptoms, please seek medical help urgently. If you have kidney impairment, you might not be able to take Mounjaro (depending on how severe it is). Speak to your clinical team to check your suitability for treatment.
Thyroid cancer
Mounjaro isn’t suitable for people with a personal or family history of thyroid cancer. In studies on rats, Mounjaro and other weight loss drugs have been linked to thyroid tumours. We don’t know whether the same applies to humans, but if you experience any concerning symptoms (think a lump in your neck, shortness of breath or trouble swallowing), don’t ignore them and seek medical help immediately.
Allergic reactions
Allergic reactions to Mounjaro are rare. But if you experience swelling of the face, rapid heartbeat, severe rash, or problems breathing, make sure to get medical help immediately. If you experience a mild skin reaction at the injection site, this is also something to mention to your doctor.
Are there any long-term side effects of Mounjaro?
Most of the time, your side effects will ease off as you adjust to the medication, or stop if you discontinue treatment. But if you are unlucky enough to experience a serious side effect, like pancreatitis or kidney damage, it might take a while before you’re better.
It’s worth noting that Mounjaro has only been on the market since 2022, with the first clinical trials taking place in 2018. That means we don’t yet have a huge trove of long-term data.
When do Mounjaro side effects start?
If you do experience side effects, they’ll probably start soon after your first injection. According to a 2023 review of the evidence, gastrointestinal symptoms tend to appear within two weeks of beginning Mounjaro, but they are typically mild and short-lived. You may also experience side effects any time you up your dose.
Some of the more serious side effects may appear at a later stage. For instance, kidney problems tend to arise after an episode of being very sick and dehydrated. Symptoms of gallbladder disease may come on suddenly. Allergic reactions, on the other hand, will appear very soon after you take the medicine.
How long will Mounjaro side effects last?
Although it’s different for everyone, you’ll probably feel much better soon. For instance, you might feel a bit queasy for the first couple of days, and then queasy again each time you increase your dose. Most of the time, your body adapts to the drug with continued use, meaning the side effects will subside.
If they don’t improve over the space of a few weeks, you should always speak to your doctor. It might be that you need to stay at a lower dose, switch to a different weight loss injection or take a short break from treatment.
Once you stop taking Mounjaro, it will be entirely cleared from your body in about 30 days. Half the medication will leave your system within five days, which should help relieve any negative symptoms.
Managing Mounjaro side effects
There are lots of practical strategies you can adopt to help reduce the side effects of Mounjaro:
For nausea:
- Eat smaller, more frequent meals
- Drink ginger or peppermint tea
- Get some fresh air
- Eat more slowly
- Steer clear of fried, greasy or strong-smelling food
- Avoid alcohol and caffeine, especially as you start treatment
- Make sure to drink lots of fluids
- Get plenty of rest
- Eat bland foods (such as dry toast) when you feel up to it
- Avoid foods and drinks that aggravate the problem (think coffee, alcohol, or full-fat dairy)
For constipation:
- Drink plenty of water
- Avoid alcohol
- Eat foods high in fibre (such as wheat bran and oats)
- Eat fruits containing sorbitol (apples, apricots grapes, raisins, raspberries, and strawberries)
- Get out for a brisk walk or run
For tiredness
- Eat little and often
- Gradually cut down on caffeine to improve sleep, especially in the afternoon and evening
- Cut down on alcohol
- Stay well hydrated
- Do things that reduce your stress levels
- Try some gentle exercise
- Take some time to relax and wind down before bed.
Always reach out to your doctor if you need further support, especially if you’re planning on taking any over-the-counter drugs to manage your symptoms.
Conclusion
Thinking about Mounjaro’s side effects can be daunting. However, it needn’t be the end of the road for your weight loss goals! Although side effects are common, most of the time they’re short-lived and unlikely to disrupt your life.
All this said, you should never feel that you have to suffer in silence. It’s really important to work with your doctor throughout your Mounjaro journey. They will help you find a dose that’s right for you—one that delivers the best possible outcomes while keeping side effects to a minimum. And remember, always call your doctor if you do experience anything concerning.
If you just want someone to talk to, Voy includes an app to track your progress, which gives you access to our clinical team. Through the Voy app, you can easily contact your coach for personalised support, advice and understanding.
FAQ
What should I do if I miss a dose of Mounjaro?
If you’re still within four days of the missed dose, take the dose as soon as you can. However, you shouldn’t take two doses of Mounjaro within three days of each other. If more than four days have gone by since the missed dose, skip this one and take the next dose on your usual day.
What if a side effect I’m experiencing is not listed?
If you experience anything that’s bothering you, always talk to your doctor.
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