Although past studies have suggested that the effectiveness of contraceptive pills are reduced when taken by obese women, a new study has revealed otherwise.

The study suggests that the birth control pill will work for all women no matter how much they weigh. The complex research was conducted by Dr Carolyn L. Westhoff of Columbia University Medical Centre in New York City. It was published in the August issue of Obstetrics & Gynaecology.

It has also been reported that obese women were 30-40% more likely to become pregnant whilst taking the pill. Many experts have suggested that excess weight may cause the contraceptive treatment to become less effective in obese people.

Dr Westhoff’s study used 226 women who were both obese, and of ‘normal’ weight. Researchers randomly assigned different strength treatments to the subjects. They were administered 3 or 4 cycles of the oral contraceptive by experts. The researchers then performed blood tests and ultrasounds on the women in order to discover whether their ovaries were still making eggs.

The study team monitored the subject’s blood levels regularly, in order to determine whether they were taking the treatment consistently. They discovered that 90% of the lighter women took the pill regularly. In comparison, only 72% of the obese women were found to be treatment consistently.

Of the 150 subjects who took the treatment consistently, 97% did not ovulate, meaning that the treatment was successful for them. They found that the weight of the women did not affect the success of the treatment.

Director of the Office of Population Research at Princeton University in New Jersey, Dr James Trussell said that “If indeed there is lower effectiveness among obese women, then this does not appear to be the mechanism through which it works.”