What are the most common tirzepatide side effects?

In SURMOUNT-1, the most common adverse events were gastrointestinal: nausea (~31% at 15mg vs ~10% placebo), diarrhoea (~23% vs 7%), constipation (~12% vs 6%), and vomiting (~12% vs 2%). All were dose-dependent and most concentrated during the dose-escalation period. Beyond GI, the prescribing information lists abdominal pain, dyspepsia, injection-site reactions, fatigue, hypersensitivity, and hair loss as labeled adverse reactions.

Are there any serious tirzepatide side effects?

Yes - the FDA-labeled serious considerations include the GLP-1 class boxed warning for rodent thyroid C-cell tumours (no confirmed human signal at population level), acute pancreatitis, gallbladder disease, acute kidney injury (dehydration-mediated), serious hypersensitivity, and worsening of diabetic retinopathy in T2D patients with rapid glucose improvement. The FDA prescribing information for Mounjaro and Zepbound is the authoritative source.

Side Effects · Research

Tirzepatide Side Effects: Hair Loss, GI & What the Trial Data Actually Shows

Q: Does tirzepatide cause hair loss?

Hair loss (telogen effluvium) was reported in SURMOUNT-1 in roughly 4-5% of the 10mg and 15mg tirzepatide arms vs ~1% in placebo. The mechanism is almost certainly rapid weight loss rather than a direct drug effect - the same shedding pattern is documented after bariatric surgery, low-calorie diets, and any major metabolic shift. It's usually temporary and resolves as weight stabilises, but it's a real reported event and was disclosed in the FDA prescribing information for Zepbound.

Q: How many people stopped tirzepatide because of side effects?

In SURMOUNT-1, discontinuation due to adverse events was ~7% in the 15mg arm vs ~3% in placebo, with GI events the dominant driver. That's lower than commonly assumed for the dose intensity. The figure rises in real-world use because trial cohorts tend to be more compliant and more monitored than typical prescriptions.

May 27, 2026 · 9 min read

"Does tirzepatide cause hair loss?" runs ~3,600 US-Google searches a month. It's not the highest-volume tirzepatide query but it's one of the most-searched side-effect questions for any peptide in the modern category. This piece walks through the actual SURMOUNT and SURPASS adverse-event data, the telogen-effluvium mechanism behind the hair-loss reports, the GI side-effect picture, and the discontinuation rates.

RUO framing throughout. Tirzepatide is the active molecule in Mounjaro (FDA-approved 2022, T2D) and Zepbound (FDA-approved 2023, obesity / OSA-with-obesity). New-U supplies the research-grade equivalent under the GLP-1 RC-T SKU as a laboratory reagent only. This article reports what the published trial data shows; it is not medical advice and is not a substitute for the FDA prescribing information.

The Hair Loss Question, Plain

Hair loss was reported in SURMOUNT-1 (Jastreboff AM et al., NEJM 2022) at the following rates:

Arm	Alopecia / hair loss
Placebo	~1%
Tirzepatide 5mg	~3%
Tirzepatide 10mg	~4.9%
Tirzepatide 15mg	~5.7%

Dose-dependent, but at relatively low absolute incidence. The signal was strong enough to make it onto the FDA-labeled adverse-reactions list for Zepbound.

The Mechanism: Telogen Effluvium

The clinical pattern is consistent with telogen effluvium - a diffuse, non-scarring hair shedding triggered when a large proportion of hair follicles shift simultaneously from the growing (anagen) phase into the resting (telogen) phase. The shedding usually starts 2-4 months after the trigger and resolves over the following 3-6 months as the follicle cycle re-synchronises.

Common triggers in the dermatology literature include:

Major weight loss - bariatric surgery, very-low-calorie diets, eating disorders
Childbirth (postpartum telogen effluvium)
Severe illness or hospitalisation
Major psychological stress
Iron deficiency, vitamin D deficiency, low protein intake

Tirzepatide-related hair loss appears to be the weight-loss trigger variant. The pattern matches what bariatric surgery and very-low-calorie diets produce. The drug itself isn't directly attacking the hair follicle; the rapid metabolic shift and reduced caloric intake are. That explains why the incidence scales with dose (because higher doses produce more weight loss) and why it's almost always reversible as weight stabilises.

The Gastrointestinal Side Effects

These are the most-common and best-documented side effects. SURMOUNT-1 incidence at 15mg vs placebo:

Side effect	15mg tirzepatide	Placebo	Pattern
Nausea	~31%	~9.5%	Worst during titration; usually improves over weeks
Diarrhoea	~23%	~7%	Dose-dependent, often transient
Constipation	~12%	~6%	Slower-gastric-emptying mediated
Vomiting	~12%	~2%	More common at higher doses
Abdominal pain	~10%	~5%	Often dyspepsia-like
Dyspepsia	~9%	~3%	Reflux-related

GI events are the dominant driver of discontinuation but are usually concentrated in the early weeks of dose escalation. Slow titration, eating smaller meals, and avoiding fatty / spicy foods during titration are the standard prescribing-information mitigations.

Discontinuation Rates

SURMOUNT-1 reported discontinuation due to adverse events as:

Arm	Discontinuation due to AEs
Placebo	~2.8%
Tirzepatide 5mg	~4.3%
Tirzepatide 10mg	~7.1%
Tirzepatide 15mg	~6.6%

Lower than commonly assumed for the dose intensity. Real-world discontinuation is consistently higher because real-world cohorts have less compliance support, less medical monitoring, and fewer mitigation tools than trial participants.

The FDA Boxed Warning & Serious Considerations

The FDA prescribing information for Mounjaro and Zepbound includes the GLP-1 class boxed warning for rodent thyroid C-cell tumours - observed in lifetime rat carcinogenicity studies. No causal human signal has been confirmed at population level, but the warning is contraindicated in personal or family history of medullary thyroid carcinoma (MTC) and multiple endocrine neoplasia syndrome type 2 (MEN 2).

Other FDA-labeled serious considerations:

Acute pancreatitis - observed in the broader GLP-1 class; discontinue if confirmed
Acute gallbladder disease - cholelithiasis, cholecystitis - elevated risk with rapid weight loss
Hypoglycaemia - particularly when combined with insulin or sulfonylureas in T2D
Hypersensitivity reactions - rare, including anaphylaxis and angioedema
Acute kidney injury - mostly dehydration-mediated through severe GI events
Diabetic retinopathy complications - in T2D patients with rapid HbA1c improvement
Suicidal behaviour and ideation - GLP-1 class signal under ongoing FDA surveillance; no causal link confirmed

What the Real-World vs Trial Picture Looks Like

Trial populations are screened, monitored, and supported in ways real-world prescribing isn't. The expected pattern in real-world use:

GI events - similar incidence to trials at population level, but higher impact because of less proactive titration management
Discontinuation rates - real-world data has reported 40-50% discontinuation by 12 months across the GLP-1 class, vs ~7% in trials. Most of that is non-AE driven (cost, insurance, supply)
Hair loss - similar incidence; reversibility consistent with trial reports as patients hit weight plateau
Serious AEs - rare in absolute terms; the absolute population-level risk of pancreatitis or gallbladder disease is lower than the absolute population-level benefit of meaningful weight loss in obese patients with comorbidities

How to Read the Hair-Loss Reports Sensibly

The incidence is real - ~5% at 15mg in SURMOUNT-1 vs ~1% placebo.
The mechanism is almost certainly the rapid weight loss, not a direct drug effect on the follicle.
It is usually temporary - telogen effluvium resolves as weight stabilises and the follicle cycle re-synchronises.
It is more concentrated at higher doses because higher doses produce more weight loss.
The same pattern is documented after bariatric surgery and other major weight-loss interventions; it's not unique to tirzepatide.
Iron, vitamin D, and protein status should be considered as contributing factors during weight loss; deficiencies worsen telogen effluvium of any cause.

Status check. Tirzepatide is FDA-approved as Mounjaro (T2D) and Zepbound (obesity / OSA-with-obesity). The data here is from published clinical trials and the FDA prescribing information. Nothing in this article is medical advice. New-U supplies research-grade tirzepatide (GLP-1 RC-T) strictly as a laboratory reagent - not for human consumption, weight-loss application, or as a substitute for prescribed Mounjaro / Zepbound. Tirzepatide is also on the WADA Prohibited List (S2).