Doctors warn of a horrifying new side effect of taking fat jabs - with the elderly and frail especially at risk

Weight-loss drugs could be linked to osteoporosis and increased risk of bone fractures, doctors have warned.

The Royal Osteoporosis Society (ROS) has expressed concern over research showing that up to 40 per cent of the weight people lose by using injections of GLP-1 agonists – such as Ozempic, Wegovy and Mounjaro – comes from their vital muscle and bone mass.

Losing muscle can impair strength and joint stability, while reduced bone density raises the risk of osteoporosis – a condition that can cause brittle bones.

Approximately half a million people in the UK now take GLP-1 drugs, with clinical trials showing they can help patients lose up to 20 per cent of their body weight. However, experts said users should be made aware of potential negative effects.

'This is an emerging field of research and people need to be warned that using these drugs increases the risk of losing bone and muscle as well as fat,' Julia Thomson, a specialist nurse with the ROS, told the Sunday Express.

'Bone and muscle health is key to preventing the risk of falling and fractures which can lead to premature death or else have a devastating effect on people's ability to live independently.'

She said it is 'essential' that fat jabs are prescribed appropriately after a discussion with a doctor.

Women are at a higher risk of developing osteoporosis, especially after menopause when a decline in oestrogen levels further accelerates bone loss.

Professor Carl Heneghan, director of Oxford University's Centre for Evidence-Based Medicine, said: 'Any drug that reduces muscle mass and bone density is a bad idea for people who are frail and those vulnerable to fractures with osteoporosis.

'The evidence is clear – these drugs carry significant risks and the longer a patient stays on them, the greater the risk.'

He said the focus should be on preventing obesity, rather than 'medicating large swathes of the population as a quick fix to the obesity pandemic'.

Recent analysis by the University of Liverpool found up to 40 per cent of the weight lost while using GLP-1 is muscle and bone.

Dr Taher Mahmud, founder of the London Osteoporosis Clinic, said: 'It is essential that those taking GLP-1 agonists know about the importance of good nutrition and weight-bearing exercise.'