GLP-1 Side Effect Q&A: Headache, Sulfur Burps, Brain Fog, Mood, Acne, and 12 Other Patient Questions

Our broader GLP-1 side effects investigation covers the headline GI tolerability numbers from STEP-1 and SURMOUNT-1. This article answers the specific Q&A queries patients search for: does semaglutide cause headaches (yes — 14.2% in STEP-1 vs 10% placebo), does tirzepatide cause sulfur burps (yes — slowed gastric emptying changes the bacterial fermentation profile), does semaglutide cause depression (no signal in the 2024 EMA review of randomized trial data, but a separate observational signal exists), does GLP-1 cause brain fog (an emerging FDA pharmacovigilance signal as of 2025). Every rate is sourced from the STEP-1 and SURMOUNT-1 NEJM publications and the Wegovy and Zepbound FDA prescribing information [1, 2, 3, 4].

The verified rate table

Verified rates from the FDA label adverse reactions tables and the published trial AE supplements [1, 2, 3, 4]:

Does semaglutide cause headaches?

Yes. STEP-1 reported headache in 14.2% of semaglutide 2.4 mg patients vs 10.0% of placebo[1, 3]. The drug-attributable rate (~4 percentage points above placebo) is real but modest — about 1 in 25 patients experiences a drug-related headache that they wouldn't have had on placebo.

The most common mechanism is dehydration. GLP-1 patients commonly drink less water (thirst is blunted along with appetite), produce slightly more nausea-related fluid loss in the early dose steps, and lose weight rapidly enough to trigger headaches in some individuals. The headache pattern usually improves once the patient stabilizes water intake and the body adapts to the maintenance dose.

What to do: increase water intake to 2-3 liters per day, watch for nausea-induced dehydration, take OTC pain relief if needed (acetaminophen or NSAIDs per your prescriber's guidance). Call your prescriber if headaches are severe, persistent past the first 4-6 weeks, or accompanied by visual changes.

Does tirzepatide cause sulfur burps?

Yes — and this is one of the most-searched and most- confusing GLP-1 side effects. The FDA label lists eructation (clinical term for burping) at ~7% on semaglutide and 2-5% on tirzepatide, vs near-zero on placebo [3, 4].

The patient-reported “sulfur burps” or “rotten egg burps” phenomenon has a specific mechanism: GLP-1s slow gastric emptying, which means food sits in the stomach longer than usual. The longer food substrate is available for bacteria in the upper GI tract, the more those bacteria can produce hydrogen sulfide gas (H₂S) — which is the chemical responsible for the rotten-egg smell. Patients with diets higher in sulfur-containing foods (eggs, broccoli, cauliflower, garlic, onions, red meat, dairy) are more likely to notice this effect.

What to do: reduce dietary sulfur load temporarily during the early dose steps, ensure smaller meals (large meals amplify the slow-emptying effect), and give the body time to adapt. The phenomenon usually improves significantly after the first 4-8 weeks of therapy.

Does semaglutide or tirzepatide cause depression?

The headline answer is no — but the evidence base is genuinely mixed and the question deserves a careful explanation.

In the STEP-1 and SURMOUNT-1 randomized trials, mood changes and depression were not elevated above placebo at any statistically meaningful rate [1, 2]. Both trials specifically tracked psychiatric AEs and neither flagged a signal.

In late 2023, anecdotal reports of suicidal ideation in GLP-1 users prompted the European Medicines Agency's Pharmacovigilance Risk Assessment Committee (PRAC) to open a formal review [6]. The PRAC concluded the review in April 2024 finding no evidence of a causal association between GLP-1 receptor agonists and suicidal thoughts or self-harm. The FDA conducted a parallel analysis and reached a similar conclusion. Neither agency added a warning to the GLP-1 labels.

However, separate observational and database studies have reported mixed signals. A 2024 large EHR cohort study reported a numerically higher depression diagnosis rate in GLP-1 users vs matched controls; other observational studies have reported no association or even a protective effect (consistent with the documented improvement in weight-related psychological burden). The discrepancy between RCT data (no signal) and observational data (mixed) is unresolved.

What to do: if you have a personal history of depression, anxiety, or suicidal ideation, discuss GLP-1 therapy with both your prescriber and a mental health provider before starting. Monitor mood actively in the first 8-12 weeks. Call your prescriber or seek urgent care if you experience persistent mood changes or thoughts of self-harm.

Does GLP-1 cause brain fog?

The trial AE tables in STEP-1 and SURMOUNT-1 do not list brain fog or cognitive impairment as a tracked adverse event [1, 2]. Brain fog is a non-specific patient-reported symptom that's difficult to measure in standard trial AE collection.

However, an emerging FDA pharmacovigilance signal exists. FAERS (FDA Adverse Event Reporting System) data analyzed in 2025 detected a reporting odds ratio (ROR) of 1.78 for cognitive complaints in GLP-1 users, with a median time- to-onset of 32 days after starting therapy. This is a signal worth knowing about but it has NOT been added to the FDA label as of April 2026 because pharmacovigilance signals are hypothesis-generating, not confirmatory.

Plausible mechanisms include central GLP-1 receptor activation in the hypothalamus and mesolimbic pathways (which can produce fatigue and lethargy), early-phase nutritional deficits during rapid caloric restriction, or dehydration. Paradoxically, longer-term observational data suggest GLP-1 use is associated with reduced Alzheimer's and dementia risk — so the brain fog signal, if real, may be transient and related to the early adjustment phase rather than a long-term concern.

What to do: monitor cognitive function in the first 8-12 weeks. Ensure adequate hydration, protein intake, and B-vitamin status. Most patients report cognitive improvement (rather than worsening) over time as weight loss progresses and metabolic markers improve. Persistent or worsening cognitive symptoms warrant a prescriber visit.

Does semaglutide or tirzepatide cause acne?

Acne is not in the STEP-1 or SURMOUNT-1 trial AE tables and is not in the FDA label adverse reactions sections [1, 2, 3, 4]. A 2025 observational cohort study reported a 36% higher acne diagnosis rate in obese women within 90 days of starting GLP-1 therapy compared to matched controls, but this is a post-hoc signal that has not been replicated in RCTs.

Plausible mechanisms include increased growth hormone secretion → increased IGF-1 → increased sebum production, and the fact that rapid weight loss in any context can transiently affect skin barrier function and oil production. The signal is more pronounced in women than men in the published cohort data, suggesting a hormonal component.

What to do: standard acne management (gentle cleanser, OTC benzoyl peroxide or salicylic acid, avoid heavy moisturizers) is reasonable. If acne is severe or persists, see a dermatologist — there's no need to stop the GLP-1 unless directed by your provider.

Does GLP-1 affect sleep or cause insomnia?

Insomnia is not commonly reported in the STEP-1 or SURMOUNT-1 AE tables [1, 2]. The opposite finding is much better documented: tirzepatide substantially improves obstructive sleep apnea in obese patients, per the SURMOUNT-OSA trial (Malhotra et al., NEJM 2024, PMID 38912654) [7]. The trial reported up to a 2/3 reduction in OSA severity at the highest dose over 52 weeks, leading to an FDA-approved Zepbound indication for OSA in obesity in December 2024.

Some patients report sleep-related symptoms like vivid dreams or temporary insomnia during the early dose steps. These are usually transient and resolve within 4-8 weeks. Sleep apnea improvement is a documented secondary benefit of GLP-1 therapy with rigorous trial evidence, while de novo insomnia is a patient-reported phenomenon without formal AE tracking.

Does GLP-1 affect libido or sexual function?

Sexual dysfunction is not in the STEP-1 or SURMOUNT-1 AE tables [1, 2]. Pharmacovigilance data reports approximately 182 case reports across all GLP-1s from 2003-2024 — a very low absolute number relative to millions of treated patients.

The much better-documented effect runs in the opposite direction: weight loss in obese patients improves sexual function across multiple domains. Bariatric surgery meta-analyses consistently show improvement in libido, erectile function, and sexual satisfaction following weight loss, and the GLP-1 weight loss magnitudes are comparable to early bariatric surgery results.

Some patients on GLP-1 therapy do report transient libido changes during dose escalation, possibly related to early nausea, fatigue, or hormonal shifts during rapid weight loss. These usually resolve as the patient stabilizes on the maintenance dose.

Does GLP-1 cause body odor changes?

Body odor is not in the trial AE tables or the FDA label adverse reactions sections. Patient-reported body odor changes do appear in online communities and may relate to: (1) altered sweat substrate composition due to dietary changes, (2) GI dysbiosis from delayed gastric emptying changing the volatile compounds in breath and sweat, or (3) ketosis-related body odor during early rapid weight loss.

This is a low-confidence patient-reported phenomenon. If you notice it, hydration, dietary fiber, and standard hygiene generally manage it.

Does GLP-1 cause cold intolerance or temperature changes?

Not in the trial AE tables. Patient-reported cold sensitivity on GLP-1 therapy likely relates to two factors: (1) loss of adipose tissue insulation during rapid weight loss reduces the body's passive insulation, and (2) reduced caloric intake decreases dietary thermogenesis (the heat produced by digesting and processing food).

Both mechanisms are well-documented in any rapid-weight- loss context (diet, surgery, drug-induced). They are not specific to GLP-1s and they typically improve as the body adapts to the new weight set point.

Does GLP-1 affect taste (dysgeusia)?

Yes, modestly. Dysgeusia (taste changes) is reported in approximately 1.7% of Wegovy patients in the FDA label adverse reactions table [3]. Patient reports often describe metallic taste, food aversions, or specific foods tasting “off.” A 2024 FAERS analysis identified ~1,469 reports of dysgeusia across all GLP-1s.

The mechanism likely involves GLP-1 receptor expression on taste receptor cells of the tongue. The effect is usually mild and transient, resolving within the first 4-8 weeks of therapy.

What red-flag symptoms require medical attention

Most of the side effects in this article are mild, transient, and self-limiting. The following symptoms are different and indicate potentially serious complications documented in the Wegovy and Zepbound labels [3, 4]:

• Severe abdominal pain radiating to the back — possible pancreatitis. Stop the drug, go to ER.
• Yellowing of skin or eyes — possible gallbladder disease. Evaluate urgently.
• Severe or persistent vomiting with dark urine — dehydration risk and potential acute kidney injury.
• Severe allergic reactions (face/throat swelling, difficulty breathing, severe rash) — stop and go to ER immediately.
• Visual changes in T2D patients — possible diabetic retinopathy progression on Ozempic/Mounjaro.
• Neck lump, hoarseness, or trouble swallowing — rare thyroid C-cell concern, label warning.
• Persistent thoughts of self-harm — call a mental health provider or 988 (Suicide and Crisis Lifeline). Stop the drug if your prescriber recommends.

Important disclaimer

This article is educational and reports the verified adverse-event rates from the published trial literature and the FDA prescribing information. Individual responses vary substantially. None of this constitutes medical advice — any persistent or severe symptom should be evaluated by your prescriber or a qualified healthcare provider. Weight Loss Rankings does not provide medical advice, diagnosis, or treatment recommendations.

Related research and tools

For the broader headline side-effect rates and management strategies, see our full GLP-1 side effects investigation. For the duration of the most-searched specific symptoms (fatigue, hair loss), see our fatigue + hair loss duration guide. For the timing context that determines when each side effect typically peaks and resolves, see our how long does GLP-1 take to work guide. For the diet adjustments that minimize the GI side effects, see our GLP-1 diet guide.