Sulfur farts on Mounjaro: what the evidence says and what you can do

What the trial data tells us about gut-related side effects

The SURMOUNT-1 trial, published in the New England Journal of Medicine, enrolled 2,539 adults and tracked tirzepatide's effects across 72 weeks at doses up to 15 mg. Gastrointestinal effects were the most frequently reported adverse events throughout the programme, nausea, diarrhoea, constipation, burping and flatulence all appeared in the trial data. The pattern was consistent: symptoms clustered around the time of starting treatment and around each dose step upward, then gradually reduced as participants continued. The NHS tirzepatide medicines page lists flatulence and stomach discomfort among the known side effects, in line with what the clinical programme found. Sulphurous-smelling gas specifically is not catalogued by name in trial data (the relevant category is flatulence and general GI disturbance) but the mechanism that produces it is the same one documented across all GLP-1 and dual-agonist medicines: reduced gastric emptying rate. Food spends longer in the upper gut before it reaches the large intestine, and by the time it arrives, the bacterial environment there has more substrate to ferment, producing hydrogen sulphide as a byproduct. The smell is the gas. It is not a sign that the medicine is failing or that something is wrong.

What makes sulphurous gas worse on Mounjaro

Two things tend to make the smell noticeably stronger. The first is diet. Foods with a high sulphur content (eggs, cruciferous vegetables like broccoli, cauliflower and Brussels sprouts, red meat, garlic, onion and some pulses) produce more hydrogen sulphide when fermented, regardless of whether you are on any medicine. On tirzepatide, because transit time is longer, bacteria have more time to work on those foods, so the effect is amplified. A practical check worth doing: scan what you ate in the 24 hours before the worst episodes. If eggs or brassicas feature heavily, a temporary reduction often produces a noticeable improvement within a day. That is not a permanent dietary restriction, it is a useful diagnostic. The second factor is the dose. Symptoms are consistently worse just after a dose increase, when the gastric-emptying effect strengthens before the body has recalibrated. People who move up too quickly can experience a sharper spike in gas and discomfort. This is one reason titration is managed by a prescriber rather than self-directed. If you are also experiencing loose stools alongside the gas, the combination of sulphurous symptoms and diarrhoea on Mounjaro is covered in more detail separately.

Practical steps that tend to help

The MHRA's reporting data and the broader clinical-practice literature point to a few consistent approaches. Eating smaller meals more slowly reduces the volume of food arriving in the stomach at once, which limits the fermentation load. Staying well hydrated helps intestinal transit; dehydration makes constipation worse and can concentrate gut gases. Avoiding fizzy drinks, which add gas before fermentation even begins, is a low-effort change. Some people find that taking Mounjaro earlier or later in the day relative to their biggest meal makes a difference, though this is something to discuss with a prescriber rather than adjust unilaterally. If burping is also prominent (a distinct but related problem) sulphur burps on Mounjaro and how to reduce them are each covered in dedicated pages. Over-the-counter remedies such as simethicone (sold for trapped wind) may offer short-term comfort for bloating, but discuss any new medicine with your prescriber first, since some agents can affect how Mounjaro is absorbed. For a broader picture of what to expect when you first begin, early side effects when starting Mounjaro covers the adjustment period in full.

When to speak to your prescriber

For most people, sulphurous wind is uncomfortable rather than medically significant, and it eases over weeks. There are situations where it warrants a proper clinical conversation. If the gas is accompanied by severe stomach pain (particularly pain that is persistent and spreads toward your back) seek urgent medical attention. This symptom combination can, in rare cases, indicate pancreatitis, which the MHRA has flagged as an infrequent but serious adverse event associated with GLP-1 medicines. A 2026 Drug Safety Update from the regulator specifically highlighted the need for patients to be aware of this presentation. Persistent, severe diarrhoea alongside wind raises the risk of dehydration, which can affect kidney function, and should be reviewed promptly. If symptoms are simply lasting longer than four to six weeks at a stable dose without improving, that is worth raising at your next clinical check-in too, a prescriber may consider whether the current titration pace suits you. The full side-effect profile of Mounjaro covers a wider range of symptoms and their clinical context. If you want to explore whether Mounjaro is appropriate for you, or if you are currently on treatment through another provider and want a clinical review, our free consultation is the starting point. You can also look at what Mounjaro costs through a private pharmacy if that question is on your mind. Every consultation at nume is reviewed the same day by a real GPhC-registered prescriber.