Nobody has measured why the burps smell of sulfur, but the burping itself is a counted side effect. In the diabetes trials behind the Ozempic label, 2.7 percent of people on 0.5 mg reported burping against none of the 262 on placebo [1]. At the 2.4 mg dose sold as Wegovy, 7 percent of 2,116 adults burped more than usual against under 1 percent on placebo [2]. In the FDA’s adverse-event database, burping was the stomach complaint most out of proportion for semaglutide, with a reporting odds ratio whose lower bound was 42.03 [3].
Picture the evening it usually starts, a few weeks after the first pen or the day after a step up in dose, when a heavy dinner comes back up as a burp that tastes like a rotten egg. That detail, the smell, is the part the labels never record, because a trial form has one box for burping and none for what the burp was like. So the answer below runs in two halves, the burping that trials and databases counted, and the sulfur that nobody has yet put a number on.
How often Ozempic and Wegovy cause burping
The Ozempic label lists burping among the less common stomach reactions, at 2.7 percent on 0.5 mg and 1.1 percent on 1 mg, drawn from two placebo-controlled trials in people with type 2 diabetes [1]. The same pool puts all stomach reactions together at 32.7 to 36.4 percent on the drug against 15.3 percent on placebo. That gives burping its scale, a small slice of a large pie and one that nausea dominates, as why GLP-1 drugs cause nausea explains.
The obesity dose moves the number up. In the Wegovy weight trials, burping reached 7 percent on 2.4 mg against under 1 percent on placebo, close to dyspepsia at 9 percent and abdominal distension at 7 percent [2]. The label adds that these reactions were reported most often during dosage escalation, the weeks when each new, higher pen arrives. The full comparison of side effects across the drugs, burping included, sits in which GLP-1 has the worst side effects.
Mounjaro and Zepbound: the same symptom in the tirzepatide tables
Tirzepatide carries the same side effect under both of its brand names. The Mounjaro label, from diabetes trials, lists burping at 3.0 percent on 5 mg, 2.5 percent on 10 mg and 3.3 percent on 15 mg, against 0.4 percent on placebo [4]. The Zepbound label, from obesity trials, lists it at 4 to 5 percent across the three doses against 1 percent of 958 people on placebo [5], high enough that it appears in the label’s own list of most common reactions.
The tirzepatide reports in the FDA database line up with those tables. An analysis of reports from 2022 to 2024 found burping and impaired gastric emptying carried the highest disproportionality of any stomach event, with most events arriving within three months and a median onset of 16 days [6]. The tables and the reports were built differently, but they point to the same early window.
What the FDA reports add, and what they cannot
The largest semaglutide analysis took 5,442 reports of stomach side effects filed to the FDA between 2018 and 2022 and found 45 signals, ranging from a lower bound of 1.01 for oral numbness to 42.03 for burping [3]. The authors describe every signal as an early failure type, meaning the risk of a new report fell as time on the drug went on, and the median onset for the strongest-priority signal was 23 days. That is a comparison of reports against reports, so it shows how distinctive burping is to semaglutide, not how many users get it.
The label rates and the database signal describe the same thing from two sides. Burping is uncommon in absolute terms, at a few percent, and it is also unusually specific to these drugs, which is why it stands out so sharply once people compare notes. The same gap between a strong reporting signal and a modest trial rate runs through the acid reflux evidence, which is the other upper-stomach complaint these drugs share.
Why the burps might smell of sulfur
The explanation that circulates is that food sits in a slowed stomach long enough for protein to break down into hydrogen sulfide, the gas that smells of rotten eggs. It is a plausible idea, and none of the sources here tested it: no study has sampled the burps of people on these drugs, and the labels count burping without recording its smell.
The slow-stomach half of the story is also less settled than it sounds. In a trial of 72 adults with obesity, 20 weeks of semaglutide 2.4 mg raised a paracetamol-absorption measure of stomach emptying by 8 percent, a difference that was no longer significant once body weight was accounted for [7]. The authors concluded there was no evidence of delayed gastric emptying at week 20, while the same people ate 35 percent less at a free lunch. The rarer, more serious version of a slowed stomach is covered in whether GLP-1 drugs cause gastroparesis, and a study that found food still in the stomach after fasting is in the gastric ultrasound log entry.
When it tends to fade
Both lines of evidence put the burping early and point to it easing. The labels tie stomach reactions to dose escalation, and the FDA analyses found reports concentrated in the first weeks, with a median onset of 23 days for semaglutide’s strongest signal and 16 days for tirzepatide [3] [6]. The dose ladder that sets those escalation weeks is laid out in the semaglutide starting dose, and the time course of the commoner stomach complaint is in how long nausea lasts on a GLP-1.
What remains unanswered is the question a person actually has at the kitchen table: whether a smaller dinner, less protein late in the day, or a slower dose step shortens the sulfur phase. No trial behind these labels reported burping by week, by meal or by how long each episode lasted, so the fading is a pattern in the reports, not a timetable anyone has measured.