Hormonal methods of contraception and intrauterine devices (IUDs) are the most effective long-term ways to avoid unwanted pregnancy.
And weight gain and weight loss were reported to be one of the adverse effects of the Pill.
According to the Institute's Director, Professor Peter Sawicki, it turns out that many researchers were too quick to jump to the conclusion that the Pill was responsible.
"Trials which systematically assessed what happens to women when they use the Pill have not proven any substantial link between hormonal contraception and weight gain," said Professor Sawicki.
"Many women gain some weight as they get older, whether or not they use the Pill. Limiting contraceptive choices will not help women keep their weight under control," he added.
Weight loss can have important health and other advantages, but the researchers believe that that there are healthy and unhealthy ways to lose weight. Many young women smoke to try to keep their weight down, for example.
"The recent withdrawal of the anti-obesity drug rimonabant in Europe on safety grounds highlights the problems that shortcuts to weight loss can cause," said Professor Sawicki.
"Other anti-obesity drugs can cause gastrointestinal problems or increase blood pressure,"
"There are no known shortcuts to long-term weight control with good health. Only a good diet and active lifestyle offer healthy long-term solutions," he added.