The world of dieting has never seen such an effective tool. Weight loss drugs like Ozempic, Mounjaro and Wegovy have been revolutionary, changing the lives of countless people struggling with obesity.

In the UK, NHS experts have warned that services are overstretched trying to deal with unprecedented demand from patients wanting to try these exceptionally effective drugs, which - originally a treatment for type 2 diabetes - have become household names.

But leading health professionals warn that these medications come with significant side effects that extend far beyond appetite suppression.

Hair loss: As the pounds shed, so can the hair. Dr Ross Kopelman, a hair transplant surgeon at Kopelman Hair Restoration, has seen a marked increase in hair thinning among patients using GLP-1 receptor agonists like Ozempic.

“Hair loss is often an overlooked side effect of rapid weight loss with these medications. While not everyone experiences it, I see it frequently enough that I always advise patients to support their hair and scalp health proactively—with proper nutrition, stress management, and sometimes targeted treatments,” he explains.

Registered trichologist and Seed & Soul founder Deborah Maguire adds: “When the body experiences a calorie deficit, it reallocates nutrients to sustain essential organs, often leaving hair follicles deprived. Weight loss medications that suppress appetite mean individuals may not consume enough of the key nutrients required to support healthy hair growth.”

Muscle loss: Muscle loss is particularly concerning for menopausal women, who are already vulnerable due to declining estrogen levels, according to Sandra Roycroft-Davis, a leading behavioural change specialist and author of the Weight’s Over.

“When weight drops rapidly due to extreme calorie restriction, the body doesn’t just burn fat—it also breaks down muscle tissue for energy. Studies on GLP-1 medications suggest that as much as 40% of total weight loss can come from lean muscle mass rather than fat,” Sandra explains.

Jordan Chadwick, managing director at Tonic Weight Loss Surgery, adds: ‘This muscle loss, known as sarcopenia, may result in decreased strength, stamina, and a lower resting metabolic rate, making long-term weight maintenance even harder.’

The aging effect: A common side effect that is common among the dieting glitterati has become known as ‘Ozempic face,’ where rapid fat loss causes facial volume depletion, leading to a gaunt, aged appearance.

Dr Naheed Ali, a physician and senior contributor at Vera Clinic, explains: “Ozempic face is not exclusive to these drugs—any significant weight loss can lead to changes in facial structure.

“But for some, the effect is more dramatic than expected.”

Gastrointestinal problems: The side effects have been well documented - and aren’t pretty.

Weight loss drugs can cause nausea, vomiting, diarrhoea, haemorrhoids and constipation, which can affect appetite, food intake, and nutrient absorption and therefore overall health.

Dom Blonska, a personal trainer and nutrition coach, has seen extreme cases: “One of my clients was bed-bound and ended up in the hospital on an IV drip for three days with gut paralysis after taking weight loss injections.”

Other side effects: Beyond hair and muscle loss, users have reported extreme fatigue and weakness, hormonal imbalances leading to missed menstrual cycles, mood swings and even, in some cases, thoughts of suicide.

A recent study showed users reported low blood pressure, including fainting, headaches, disturbed sleep, kidney stones, inflammation in the kidneys and a range of bone or joint pains and potentially deadly inflammation in the pancreas.

Experts stress that potential users should address any underlying health issues before trying the jabs.

”There is no quick fix,” Blonska warns.

“If your hormones are out of balance, weight loss drugs may make things worse.’”

The physiological impact: If you stop taking weight loss drugs, weight often returns—sometimes rapidly. Ashley O’Driscoll, a mum of one, has been taking Ozempic for nearly 18 months, but she had to stop taking it when her finances changed, meaning she could no longer afford to spend £147 a month.

For around six months – when she was totally Ozempic free – Ashley put on over two stone.

“I’d literally eat anything I could get my hands on. You have a lot of cravings when you’re not on Ozempic,” she said.

But despite all this, studies have also suggested that weight loss drugs can significantly improve health, with one wide-scale study linking them to better heart health, fewer infections and fewer cases of dementia.

So it seems the jury is still out.