Does semaglutide or tirzepatide cause hair loss? What the research says

What the trials found

Hair loss is a side effect that trials record when participants mention it. It is usually listed as "alopecia", a broad word for any hair loss, without a dermatologist confirming the type.

SURMOUNT-3 (tirzepatide). Adults with obesity, or overweight plus a weight-related condition, and without diabetes, first lost an average of 6.9% in a 12-week intensive lifestyle program. They were then randomized to tirzepatide (10 or 15 mg) or placebo for 72 weeks. People on tirzepatide lost a further 18.4%.¹

That was 20 of 287 people on tirzepatide and 4 of 292 on placebo.¹

The pivotal trials, pooled. A 2025 joint advisory from four US nutrition and obesity societies summarized the common side effects listed in the prescribing information for both medicines:²

Semaglutide across many trials. A 2026 meta-analysis pooled nine randomized comparisons of semaglutide in different conditions. Hair loss was reported by 1.65% of people on semaglutide and 0.37% of comparators, roughly three times the odds. The authors rated the certainty as low, because many trials do not report hair loss consistently.³

Why it might happen

Two recent reviews by dermatologists looked at trials, cohort studies and adverse-event reports.^4,5 When the type of hair loss was recorded at all, two patterns came up most:

• Telogen effluvium (TE). A stress on the body pushes many hairs into their resting phase at once, and they fall out together. It shows up as diffuse shedding, typically 2–3 months after the trigger.⁵ Acute TE usually lasts less than six months and is reversible.⁴ It is well known after bariatric surgery and strict diets.
• Androgenetic alopecia. Inherited pattern thinning. The reviews suggest a bout of TE may unmask or speed up thinning that was already starting.⁴

The leading theory is that the cause is mostly the weight loss and low intake, not the drug acting on hair directly. One review points out that the risk of TE with tirzepatide in a large health-record study was similar to the risk after bariatric surgery, which suggests that weight-loss dynamics, not the drug class itself, drive the risk.⁴ The same review lists low vitamin D, iron, calcium and protein as possible contributors, and notes that women seemed to be affected more often.⁴

What is not known

• Cause is not proven. No large trial was designed to study hair, and most reports did not record what type of hair loss it was.^4,5
• A direct drug effect is untested. The Am J Clin Dermatol review notes that no human study has examined the role of the GLP-1 receptor in how hair follicles grow.⁵
• Open questions remain about who is most at risk and how timing relates to the drug. The reviewers call for large prospective trials to settle cause.⁴ Whether slower weight loss or better nutrition prevents it has not been tested.
• Evidence is mixed. Some studies even describe regrowth in certain hair conditions, while more link GLP-1s with TE.⁵

What this means in practice

• Note the timing. Shedding that starts a few months after a big drop in weight fits the TE pattern. Writing down when it started, and how fast your weight was falling, helps your doctor sort out the cause.
• Ask about blood tests. One review lists low ferritin, low vitamin D and abnormal thyroid tests as common findings in TE, and suggests a dermatology referral if the picture is unclear or nothing improves after 3–6 months.⁵
• Keep protein up. Low intake is one suspected trigger, and protein often drops when appetite does. See what the research says about protein.
• Talk before you stop. If hair loss makes you think about stopping, raise it with your prescriber first. Weight tends to come back after stopping; see what the trials found.