Obesity drug may burn calories by activating brown fat

A blockbuster obesity drug may be helping people lose weight in a way scientists had not fully understood before. New research has found that tirzepatide, a medicine already known for reducing appetite and body weight, can also activate the body’s calorie-burning “brown fat”, opening a new front in the fight against obesity.
The findings were presented at ENDO 2026 recently, the annual meeting of the Endocrine Society, and are being seen as an important step towards understanding how modern anti-obesity medicines work beyond simply reducing food intake. Tirzepatide, under the brand name Mounjaro was launched in India in March last year by US-based pharma giant Eli Lilly and has been the country’s top-selling medicine brand by value since October 2025. Last month, the drug also became the highest selling medicine brand globally.
The molecule belongs to a comparatively new class of medicine called GLP-1 based therapy, like semaglutide, which was first developed against type 2 diabetes but has gained immense popularity due to rapid weight-loss effect.
These drugs work by mimicking gut hormones, slowing digestion and reducing appetite and are now being studied for a number of conditions including cardiovascular and metabolic conditions, kidney and brain diseases and even cancers.
The latest evidence shows that unlike white fat, which stores excess calories in the body, brown adipose tissue, commonly called brown fat, helps burn calories to generate heat. Scientists have long known that brown fat plays a role in energy expenditure, but its activity is usually reduced in people living with obesity.
Researchers conducted a randomized, placebo-controlled clinical trial involving premenopausal women with obesity. Participants received tirzepatide treatment for 24 weeks, while a separate group received a placebo. Advanced imaging techniques, including PET/CT scans and MRI scans, were used to measure brown fat activity before and after treatment.