The link between the contraceptive pill and weight gain has been dubbed a myth.
Scientists looked at a group of rhesus macaque monkeys, which have a reproductive system that is almost the same as a human's, from the Oregon National Primate Research Center in order to make the claim.
Half of the sample group of monkeys were of a normal weight when the study began, while the other half were obese.
All were given oral contraceptives in doses according to their body mass.
Over the course of eight months their nutritional intake, levels of physical activity, lean muscle mass and body fat mass were monitored as they took the pill.
The results showed that the monkeys that were obese lost an average of 8.5 per cent of their body weight and 12 per cent of their body fat as a result of a higher basal metabolic rate, while those with a normal weight remained the same.
Senior author Judy Cameron commented: "This study suggests that worries about weight gain with pill use appear to be based more on fiction than on fact.
"Additionally, there may be a differential affect depending on your starting weight - heavier individuals who keep their diet stable may see a weight loss with pill use."