A new pill designed to improve body composition has shown promising early results in human testing.
The drug, called ATR-258, reduces body fat while increasing muscle mass at the same time. Developed by biotechnology company Atrogi, it works by targeting skeletal muscle through a biased signalling mechanism, activating pathways involved in muscle growth.
The treatment is still in the early stages of development, but an initial clinical trial has produced encouraging results.
Researchers tested ATR-258 in 13 overweight or obese men as part of a University of Copenhagen study. Participants took the pill once a day for eight weeks.
On average, they lost 1.1kg of fat, gained 0.8kg of lean mass and improved their leg strength by 13%.
The findings surprised even principal investigator Morten Hostrup.
With extensive experience researching the pathways targeted by the drug, he hadn’t expected to see such a large improvement in lower-body power.
‘What struck me most was the magnitude of the signal in lower-extremity power. I know they [molecules in the drug] can enhance power, but not to the extent we observed here. These findings give us a genuinely intriguing signal about the role of biased signalling in muscle physiology, and a strong rationale for taking ATR-258 forward into larger clinical trials,’ he said.
With the growing popularity of GLP-1 medications – which can lead to losses of both fat and muscle mass – alongside the rising prevalence of sarcopenia and other muscle-wasting conditions, ATR-258 could eventually become an important therapeutic option.
However, the treatment remains experimental and isn’t intended as an alternative to resistance training for otherwise healthy people.
‘These first clinical data give us important confidence that our approach is translating,’ said Professor Tore Bengtsson, Chief Scientific Officer and founder of Atrogi.
‘To see fat loss alongside an increase in lean muscle mass and improvement in muscle function represents a truly differentiated profile, and is highly encouraging.
‘Beyond muscle-sparing weight loss, we believe this mechanism also warrants investigation in sarcopenia and rare diseases marked by substantial muscle loss and weakness.’
The next stage of testing is expected to begin in 2027, when researchers hope to demonstrate proof of concept in a larger group of participants.
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Ryan is a Senior Writer at Men’s Health UK with a passion for storytelling, health and fitness. Having graduated from Cardiff University in 2020, and later obtaining his NCTJ qualification, Ryan started his career as a Trainee News Writer for sports titles Golf Monthly, Cycling Weekly and Rugby World before progressing to Staff Writer and subsequently Senior Writer with football magazine FourFourTwo.
During his two-and-a-half years there he wrote news stories for the website and features for the magazine, while he also interviewed names such as Les Ferdinand, Ally McCoist, Jamie Redknapp and Antonio Rudiger, among many others. His standout memory, though, came when getting the opportunity to speak to then-Plymouth Argyle manager Steven Schumacher as the club won League One in 2023.
Having grown up a keen footballer and playing for his boyhood side until the age of 16, Ryan got the opportunity to represent Northern Ireland national futsal team eight times, scoring three goals against England, Scotland and Gibraltar. Now past his peak, Ryan prefers to mix weightlifting with running – he achieved a marathon PB of 3:31:49 at Manchester in April 2025, but credits the heat for failing to get below the coveted 3:30 mark…
You can follow Ryan on Instagram @ryan.dabbs or on X @ryandabbs_