"Available evidence is insufficient to determine the effect of combination contraceptives on weight, but no large effect is evident," researchers have concluded. The findings, based on analysis of more than 40 trials, suggest that women can be reassured that substantial weight gain should not occur if they use such contraceptives.

Weight gain is considered by many women and physicians to be a side effect of combination (estrogen and progestin) contraceptives, and is commonly cited as the main reason for discontinuing, or not initiating, use. Even the perception of weight gain can be enough to prompt discontinuation: in one study, women who discontinued oral contraceptive use were more likely to report weight gain than those who continued use, despite there being no statistically significant difference in weight gain between the two groups.

Several mechanisms have been proposed for how combination contraceptives could lead to weight gain, through potential effects on fluid retention, muscle mass, and fat deposition. But a causal relationship has not been established.

To investigate the association between combination contraceptive use and change in body weight, specialists from Leiden University Medical Center in the Netherlands, and from Family Health International in Durham, North Carolina, USA, performed a systematic review of randomized controlled trials. Three of the trials identified and considered suitable for inclusion in the review were placebo controlled, while 40 trials compared two or more combination contraceptives.

No large effect seen

Reporting their findings in the latest issue of the journal Obstetrics & Gynecology, the researchers say the three placebo-controlled trials provide no evidence supporting a causal association between combination contraceptives and weight gain. But they acknowledge: “Given the numerous combination contraceptive drugs, doses and regimens, the possibility that one or more combination contraceptive could cause weight gain cannot be eliminated with data from these three placebo-controlled trials.”

The researchers also report that most of the comparisons of different combination contraceptives showed no substantial difference in weight or in discontinuation rates due to weight gain.

They conclude that if there is any causal association between use and weight gain, it is small. “Health care providers can reassure women that substantial weight gains have not been demonstrated in women using combination hormonal contraceptives,” the researchers write.

Source: Obstetrics & Gynecology 2004; 103: 359-73, Issue 03: 23 Feb 2004