People who switched from Novo Nordisk's injectable Wegovy to Lilly's oral Foundayo regained an average of 900gms after a year, according to a study presented at the European Congress on Obesity in Istanbul on Tuesday.
Patients who switched to Foundayo from Lilly's own more potent injectable Zepbound regained an average of five kilos.
Lilly introduced its new oral medication, a competitor to Danish drugmaker Novo's Wegovy pill, in the US market in April, as the Indianapolis-based drugmaker continues to push its big bet on obesity and diabetes medications from a drug class known as GLP-1s.
The World Health Organisation has declared obesity is now a global public health crisis with more than one billion people living with the condition.
Analysts have forecast sales of weight-loss medications reaching over $US100 ($A138) billion a year in the next decade.
Lilly said the trial demonstrates that patients can make a switch and still keep most of the weight off, a particular concern with stopping GLP-1 injections.
"If you're a patient on Wegovy, you can switch from a GLP-1 injectable to a GLP-1 pill and basically keep all the weight off," Kenneth Custer, Eli Lilly's president of cardiometabolic health, said in an interview.
"Patients now have options."
The study looked at patients switching to Foundayo, known chemically as orforglipron, after 72 weeks of losing weight on Lilly's tirzepatide, sold as Zepbound and Mounjaro, or injectable semaglutide, Novo's Wegovy and Ozempic.
At 52 weeks after the switch, prior tirzepatide users had maintained 74.7 per cent of body weight reduction with orforglipron, compared with 49.2 per cent for those who received a placebo.
Previous semaglutide users had maintained 79.3 per cent of body weight reduction with orforglipron, compared with 37.6 per ent for the placebo group.
Novo launched injectable Wegovy in 2021 and the pill version earlier this year. The pills have been expected to open the class of drugs to new patients, including those opposed to using needles.
