Sulphur Burps and Diarrhoea on Mounjaro: Separating Myth from Reality

The biggest misconception: sulphur burps mean Mounjaro isn't working or isn't safe

One of the questions our prescribers hear most regularly is whether eggy burps and diarrhoea mean something has gone wrong with the medicine or the supply. The answer is almost always no. These symptoms are a predictable consequence of how tirzepatide works, not evidence of a faulty pen or a problem with the drug itself.

Tirzepatide activates two gut-hormone receptors (GIP and GLP-1) which among other effects slow gastric emptying. Food spends longer in the stomach than it normally would. That extended transit time allows more bacterial fermentation of sulphur-containing compounds (from eggs, meat, garlic, onions and cruciferous vegetables), producing the hydrogen sulphide gas behind eggy or sulphur-tasting burps. The same slowdown can then speed up movement through the lower gut as the body compensates, which is why loose stools or diarrhoea and sulphur burps on Mounjaro often appear together, something our dedicated page explores in full. The NHS tirzepatide page lists diarrhoea as one of the more commonly reported side effects, alongside nausea, constipation and indigestion.

The symptoms are real and can be genuinely disruptive. They are also, for most people, temporary. If you want to understand how sulfur burps and diarrhea on Mounjaro tend to develop and what you can do about them, our dedicated page covers the detail. Adjusting what you eat in the days around your injection (reducing high-sulphur foods, eating smaller meals more slowly) is a practical checking habit many people find useful, and it takes about thirty seconds to scan your plate before sitting down.

If you want a fuller picture of how tirzepatide behaves in the body, the Mounjaro overview on our site covers the mechanism in more detail.

When diarrhoea and sulphur burps on Mounjaro are likely to happen, and for how long

Timing matters. Mounjaro diarrhoea and sulphur burps tend to cluster around two moments: the first few injections on a new dose, and the days immediately after each weekly injection as tirzepatide peaks in the bloodstream. This is not the same as continuous daily diarrhoea that never lets up.

If your symptoms started with your very first pen at 2.5mg, you are not unusual. The starter dose is intentionally low to give your digestive system time to adapt, but some people still notice GI effects even at that level. If symptoms appear or worsen each time you move up the titration schedule, that is the same mechanism repeating. Most people report that things settle within one to fourteen days at each dose level as the gut adjusts.

What tends to prolong symptoms: eating large portions, fatty or very rich food, high-sulphur ingredients in the days around the injection, and not drinking enough water. Mild dehydration is a real risk when diarrhoea is frequent; sipping fluids steadily through the day rather than in large gulps is worth doing. If diarrhoea is severe enough that you cannot keep fluids down, that moves into the territory your prescriber or GP needs to know about promptly.

For a closer look at why sulphur burps are such a common experience on Mounjaro, that page goes into more depth on dietary triggers and what tends to help.

When to get medical help, and what the MHRA flags as serious

Most diarrhoea and sulphur burps on Mounjaro resolve without medical input. Some situations are different. Seek urgent help if you experience severe stomach pain that does not pass and spreads toward your back, particularly if it comes with vomiting. This combination can indicate acute pancreatitis, a known but uncommon side effect of GLP-1 medicines. In January 2026 the MHRA issued a Drug Safety Update specifically highlighting pancreatitis as a serious infrequent risk with this class of medicine, and confirmed that people should seek urgent care for that symptom pattern.

Other symptoms that warrant a call to your GP or 111: diarrhoea lasting more than a few days without improvement, signs of dehydration (very dark urine, dizziness, dry mouth), blood in stools, or sudden development of severe GI symptoms that feel different in character from the mild nausea you had before.

Dizziness is occasionally reported alongside GI symptoms on Mounjaro; our page on dizziness as a Mounjaro side effect explains when it is likely to be dehydration-related and when it needs assessment. If you are unsure whether what you are experiencing is within the expected range, you can also report it to the MHRA through the Yellow Card scheme, the scheme is open to patients, not just clinicians, and every report contributes to the ongoing safety picture for tirzepatide.

For a broader overview of what the full side-effect profile looks like across all doses, our Mounjaro side effects page covers the complete picture.

How your prescriber can help if symptoms are stopping you from continuing

GI side effects are the most common reason people consider stopping Mounjaro earlier than planned. That would be worth discussing before making any decision. There is usually something that can be tried first: adjusting the injection day, reviewing your diet around the injection, or in some cases slowing the titration pace.

At nume, every repeat order goes through a fresh clinical review by a GPhC-registered prescriber, not an automated system. Side effects come up in that review regularly, and it is exactly the right place to raise them. If ongoing symptoms are affecting your quality of life, our prescribers discuss the options as part of your assessment. You can also reach the aftercare team through our contact page seven days a week.

If you are exploring treatment and want to understand the full picture before starting, speak to our prescribers through the free consultation; side-effect profiles, your medical history and suitability are all part of that conversation from the beginning.