( CNN ) -- A relatively obscure drug used to treat mouth sores has made obese mice thin -- and the mice did n't have to eat less or exercise more , according to a study at the University of Michigan . Doctors at the university will begin studies in human beings later this year . Hopes are high , even though many drugs that work in mice do not work in humans . `` It is a tour de force and offers a new and potentially exciting opening for developments of new anti-obesity drugs -- something which is badly needed , '' says Dr. George Bray , chief of the Division of Clinical Obesity and Metabolism at Pennington Biomedical Research Center at Louisiana State University . In the study at the University of Michigan , researchers gave mice a high-fat diet , and they became obese . They then injected the animals with a drug called amlexanox , which has been on the market for more than 15 years to treat canker sores . The mice lost weight , even though they kept eating the same number of calories . When they were taken off the drug , the mice gained all the weight back . If amlexanox works in humans -- and that 's a big if -- Bray said it could become like the story of Viagra , which was originally developed to treat one condition , chest pain , but serendipitously was later found to treat a different condition , erectile dysfunction . `` It could well be that what works for one disease will turn out to work for another , even though that was n't the original intent , '' he said . The researchers screened several drugs and found that amlexanox , used in an ointment to treat canker sores , changed the action of genes that control metabolism . When injected in mice , the drug worked by increasing metabolism , not by suppressing appetite . `` One of the reasons that diets are so ineffective in producing weight loss for some people is that their bodies adjust to the reduced calories by also reducing their metabolism , so that they are 'defending ' their body weight , '' says Dr. Alan Saltiel , the lead researcher at the University of Michigan . `` Amlexanox seems to tweak the metabolic response to excessive calorie storage in mice . '' The findings were published Sunday in the journal Nature Medicine . Clinical trials are expected to begin later this year to test the drug 's effectiveness in humans . In the mouse study , the researchers took pains to make sure that it was the drug , and not something else , that was making the mice lose weight . They used a laser machine to trace the mice to see if perhaps the weight loss was because they moved around more while on the drug . `` They do n't move more . The movement is exactly the same . The increased energy expenditure was due to something called thermogenesis , meaning they generate a little bit of heat , '' Saltiel said . If the drug helps humans lose weight , researchers would have to make sure it 's safe . `` One concern will be whether these drugs , by increasing energy expenditure and body temperature , may have unintended consequences on other systems , such as the heart . '' Experts say that 's an especially important concern because if the drug is ever used in humans for weight loss , patients would likely need to stay on the drug indefinitely , or else see the weight return .
Study : Obese mice given a canker sore drug lost weight without cutting calories , moving more . Doctors will begin testing the drug , amlexanox , in humans later this year . If the drugs works , it could be like Viagra , which originally was meant to treat chest pain .