GLP-1 medicines and hair loss

Four months after the first injection, the scales show fifteen kilos less. Then one morning, the shower drain is full of hair. So is the brush. Many people taking semaglutide or tirzepatide, medicines from the GLP-1 agonist family, ask the same question: is it the medicine? Most of the answer lies in the weight they’ve lost.

What the official labels say

Hair loss is one of the official side effects of these medicines. The European label for semaglutide for weight management lists it as “common”, meaning it affects between 1 and 10 people in 100¹. In trials, it was reported by 2.5% of treated people, against 1.0% on placebo, and by 5.3% on the highest dose¹. Cases were mostly mild, most people recovered without stopping treatment, and hair loss was more frequent in those who had lost at least 20% of their body weight¹.

The US label gives similar figures: 3.3% on semaglutide against 1% on placebo, and 4% against 2% among women². It states that these cases “were associated with weight reduction”².

For tirzepatide, the gap between women and men is clear.

Here too, the label links hair loss to weight loss³. The European label for tirzepatide also lists it as common, mainly in people treated for overweight or obesity⁴. In the UK, the NHS lists it among the common side effects of semaglutide⁵.

These figures come from trials designed to measure weight loss, not from studies of hair.

Why losing weight fast makes hair fall out

A hair grows for years, rests for a few months, then falls out to make room for the next one: that’s the hair cycle. It’s why everyone loses 50 to 100 hairs a day without noticing⁶.

A shock to the body can push a lot of hairs into the resting phase at once. The American Academy of Dermatology lists losing 20 pounds (about 9 kilos) or more among these triggers, alongside childbirth, a high fever or surgery⁶. Dermatologists call this telogen effluvium. The shedding becomes visible 2 to 4 months after the trigger, and can affect up to half the hair on the scalp⁷. It’s the same mechanism as the hair loss that follows a crash diet.

Eating much less can also lead to shortfalls. The American Academy of Dermatology points out that too little iron, protein, zinc or biotin can cause hair loss, and that hair can grow back once the shortfall is corrected⁸. With your appetite cut for months, that risk is real.

Does the medicine act on hair?

A systematic review published in 2026 brought together 24 studies on the subject⁹. In the tirzepatide weight-management trials, hair loss affected 5.4% of treated people, against 0.9% on placebo⁹.

The authors are cautious about the cause. So far, no study in humans shows that these medicines act directly on the hair follicle⁹. The data point to a link with weight loss, but the medicine’s own effect remains hard to separate from its effects on metabolism⁹. Some evidence suggests women are more affected, though it’s unclear whether that’s biological or because they report it more often⁹.

The review has its own limits, which the authors describe: studies that differ widely from one another, and pharmacovigilance reports that measure what is reported, not how often it really happens, and don’t prove cause and effect⁹.

How long it lasts

The review’s authors note that shedding can start about 2 to 3 months after beginning treatment, and that it generally improves 3 to 6 months after weight stabilises⁹. For telogen effluvium in general, shedding gradually tapers back to normal over 6 to 9 months in most cases⁷. If the trigger continues, it can last longer⁶. So while you’re still losing weight fast, the shedding may carry on.

The follicle isn’t damaged. The hairs that fall make way for new ones, which will take months to grow back to length⁷.

What helps while it lasts

• Eating enough protein, fruit and vegetables, even with little appetite⁷.
• Handling your hair gently: no vigorous brushing or combing, no firm scalp massage⁷.
• Having a blood test check iron, vitamin B12, folate and thyroid function, and correcting anything that’s low⁷. We go through what’s known about each deficiency in another article.

Don’t change your treatment on your own because of hair loss. It’s up to the doctor who prescribes it to decide whether anything should change: in severe cases, the review mentions adjusting or temporarily pausing treatment, decided by the doctor⁹.

When to talk to your doctor

Repeated episodes of effluvium can sometimes lead to female pattern hair loss⁷. Only a doctor can tell the two apart. We sum up the signs that mean it’s time to see a doctor about hair loss.

Tracking your hair during treatment

On a weight-loss treatment, everything changes at once: your weight, your face, your appetite. You check your hair in the bathroom mirror, under different light every day. It’s hard to tell whether the shedding is slowing down.

One photo a week, same light, same angle, hair dry, gives a more reliable answer. In Calvap, last week’s photo shows as an overlay so you can line up the shot. The journal keeps the date of your first injection, treatment changes agreed with your doctor and your blood tests. On the same timeline, you see when the shedding started, and from when your volume comes back.