At first, Nour Mansour was thrilled by the effects of weight-loss jab Mounjaro – dropping from a size 18 to a size 8 in less than seven months.

The 28-year-old had struggled with her weight since the birth of her twin daughters, now four, and was amazed by the sudden boost in confidence.

But six months in, she noticed a disturbing side effect. Her hair – once full and falling nearly to her hips – began shedding at an alarming rate.

‘I’d run my hands through my hair and clumps would fall out,’ said the administration assistant from London.

‘I’m Middle Eastern so my hair is my treasure, but it quickly went from glossy and thick to dry and frizzy. At the front, my temples were getting very empty, so I started wearing caps and headbands all the time. It was awful.’

Nour is far from alone. A swathe of Mounjaro users have taken to social media forums to share their concerns about hair loss – with some even stopping the injections as a result.

Last month, former politician Nadine Dorries revealed her own experience in her Daily Mail column. ‘Being a former nurse, I had made sure I checked out every possible side effect before injecting myself for the first time,’ she wrote. ‘What I didn’t read about anywhere – and what didn’t appear to have been known at the time – was the distressing possibility of hair loss.

‘It knocked me sideways to such an extent that I told no one about it.’

Nour Mansour, 28, noticed her hair was falling out six months after starting Mounjaro

‘‘I’d run my hands through my hair and clumps would fall out,’ said Nour

Recent trials have shown that all weight-loss GLP-1 drugs can cause hair loss, with Mounjaro among the worst offenders – over five per cent of users reported hair shedding.

But experts believe the medication does not cause the problem.

Dr David Fenton, consultant dermatologist at OneWelbeck and a world-renowned hair loss specialist, says: ‘Rapid weight loss or sudden dietary changes can leave people deficient in the nutrients essential for healthy hair growth.

‘These include iron, vitamin B12, folate, zinc and vitamin D. When users lose their appetite and start eating less, they risk missing out on key vitamins.’

A lack of protein can also be a factor, he adds, as hair is primarily made from keratin – a protein. Without enough, hair becomes weak and brittle. Other side effects seen in GLP-1 users, such as brittle fingernails and slowed nail growth, have also been linked to deficiencies.

Dr David Strain, a diabetes expert at Exeter Medical School, says: ‘During trials, participants are closely monitored and kept on a nutrient-rich diet. But in the real world, many people simply don’t know how to meet their nutritional needs or what supplements they might require.’

Anyone concerned about hair loss should consider a blood test, particularly if they follow a vegan or vegetarian diet, says Dr Fenton. Iron can be found in red meat, seafood, dark leafy greens and nuts. Dairy, eggs and wholegrains are good sources of zinc, while B12– found primarily in animal

products – is widely available in supplement form.

‘Normally, about 90 per cent of the hair follicles on your scalp are growing and 10 per cent are resting,’ said Dr Fenton. ‘But when

the body is under stress – from illness, fever or significant weight loss – that cycle shifts, and more follicles go into the shedding phase. The more weight you lose, and the faster you lose it, the higher the risk.’

This condition is known as telogen effluvium, characterised by thinning and increased hair fall during brushing or washing.

It’s similar to postpartum hair loss in women, and while the severity varies between individuals the issue usually resolves itself over time.

‘I’m Middle Eastern so my hair is my treasure, but it quickly went from glossy and thick to dry and frizzy.’

There are, however, steps that can help to minimise damage.

‘Any nutritional deficiency will slow recovery,’ says Dr Fenton. ‘If you’re underweight or lacking essential nutrients, your hair may not return to its former thickness.’

Slowing down weight loss can also help, as it reduces the stress on the body.

Estates manager Grace Parkin, 34, saw her hair loss ease after improving her diet while using Mounjaro.

The mum-of-one from Sheffield lost seven stone in a year, but started noticing that her hair was thinning just three months into using the drug.

‘I was definitely guilty of not eating enough in the beginning because I just wasn’t hungry,’ she says.

‘Now I make a conscious effort to have a good, balanced diet – and I’ve seen my hair start to grow back.’

Nour had a similar turnaround. After speaking to her GP, she began taking supplements and focused on eating well – and the shedding stopped.

‘For most people, hair will grow back,’ says Dr Fenton. ‘But if you’re eating properly and it’s still falling out, speak to your GP.’