Starting a Weight-Loss Injection - What to Know About Your Hair

Weight-loss injections such as semaglutide (sold as Wegovy for weight management and Ozempic for type 2 diabetes) and tirzepatide (Mounjaro) have become some of the most talked-about medicines in the UK. Alongside the conversations about appetite and results, one question comes up again and again online: will it make my hair fall out?

The honest answer is that some people do notice extra shedding while taking these medicines, but the picture is more nuanced than many social media posts suggest. This article sets out what the official information says, why hair shedding can happen during significant weight loss, and some practical questions worth discussing with your prescriber.

What the official information says

In the UK, the product information for each licensed medicine, known as the Summary of Product Characteristics (SmPC), lists the side effects seen in clinical trials. The SmPC for Wegovy, published on the Electronic Medicines Compendium, lists hair loss as a side effect. It reports that hair loss occurred in 2.5% of people treated with semaglutide 2.4 mg, compared with 1.0% of those on a placebo. It also states that hair loss was reported more often in people who lost a greater amount of weight, that most cases were mild, and that most people recovered while continuing treatment.

The NHS medicines page on semaglutide also includes hair loss among its listed side effects, and the NHS page on tirzepatide sets out the side effects for that medicine.

Put simply, extra shedding is a recognised side effect at weight-loss doses, but it affects a minority of people, and in trials it was usually mild and temporary.

Why losing weight can affect your hair

Most hair shedding linked to these medicines appears to be connected to the weight loss itself rather than to the medicine attacking the hair follicles. Rapid or significant weight loss is a well-known trigger for telogen effluvium, a type of temporary shedding in which a larger than usual number of hairs enter the resting phase at the same time and then fall out a few months later.

This has been recognised long before weight-loss injections existed. A 2024 study in the Annals of Dermatology looked at 140 people with telogen effluvium following weight loss from a range of causes. On average, shedding occurred after people had lost around 15% of their body weight, at a rate of roughly 3.5 kg per month. The researchers also found that women and older adults appeared more vulnerable, even when they had not lost more weight than men or younger adults.

This helps to explain why the Wegovy trials found hair loss was more common in people who lost more weight. The more quickly and significantly the body changes, the more likely the hair cycle is to be disrupted.

Other factors that may play a part

Because these medicines reduce appetite, some people end up eating much less than they realise. If that means too little protein, iron or overall energy, it may add to the strain on the hair cycle. Hair is not essential for survival, so when the body is under nutritional pressure, hair growth is one of the first things to be deprioritised.

It is also worth remembering that other things can happen at the same time. People starting these medicines may be making other changes to their diet, stopping or starting other medicines, or dealing with health conditions such as thyroid problems or diabetes, all of which can affect hair in their own right.

Questions worth asking before and during treatment

If you are starting, or already taking, a weight-loss injection and you are concerned about your hair, these are sensible topics to raise with your prescriber:

• What is a realistic rate of weight loss for me? Faster is not always better, and a steadier pace may be easier on the body overall.
• How can I make sure I am eating enough protein and nutrients? Ask whether a referral to a dietitian or specific dietary guidance would help.
• Would any blood tests be useful? If shedding starts, checking things such as iron stores and thyroid function can rule out other causes.
• What should I do if I notice shedding? In most cases, the advice will not be to stop the medicine, but that is a decision to make with your prescriber rather than on your own.

If you notice more hair falling out

A few points are worth keeping in mind:

• Timing matters. Shedding linked to weight loss tends to appear some weeks or months after the weight loss has begun, so it may not line up neatly with starting the medicine.
• Look at the pattern. Weight-loss shedding usually causes thinning across the whole scalp. Distinct bald patches, a sore or inflamed scalp, or thinning concentrated in one area point to something else and should be checked by a GP.
• Do not stop your medicine without advice. Speak to the person who prescribed it first.
• Report side effects. In the UK, anyone can report a suspected side effect of a medicine to the MHRA through the Yellow Card scheme. Reports help regulators build a clearer picture of how medicines affect people in everyday use.
• Buy only from legitimate sources. Prescription weight-loss medicines should come from a registered pharmacy with a valid prescription. Products bought from unregulated sellers may not contain what they claim.

Will the hair grow back?

For shedding caused by telogen effluvium, the outlook is generally good. The hair follicles are not destroyed, and once weight stabilises and the body adjusts, the hair cycle tends to return to normal. The Wegovy product information notes that most people in the trials recovered while continuing treatment.

Regrowth is gradual, and because hair grows slowly, it can take several months before the difference is visible. If your hair has not recovered within six months or so after your weight has stabilised, or if you notice thinning in a particular pattern, it is worth asking your GP whether something else might be involved, such as inherited pattern hair loss that the shedding has made more noticeable.

A note for anyone considering hair restoration

Some people who have lost weight on these medicines go on to consider longer-term hair loss treatments. It is generally sensible to wait until your weight is stable and any shedding has settled before making decisions, as it can be difficult to judge the true extent of any permanent hair loss while the hair cycle is still recovering.

The bottom line

Hair shedding is a recognised but relatively uncommon side effect of weight-loss injections, and it appears to be linked mainly to how much and how quickly weight is lost. For most people it is mild and temporary. Talking to your prescriber about a sensible rate of weight loss and good nutrition, keeping an eye on the pattern of any shedding, and reporting side effects through the proper channels are all practical steps.

For a closer look at the evidence on semaglutide and hair, including the difference between the diabetes and weight-loss doses, see this guide to Ozempic and hair loss from My Hair UK.

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