The WHO multicentre trial of the vasopressor effects of combined oral contraceptives: 2. Lack of effect of estrogen. Task Force on Oral Contraceptives. WHO Special Programme of Research, Development and Research Training in Human Reproduction.

Changes in blood pressure were measured in a randomized double-blind trial of 680 women using oral contraceptives containing either 50 or 30 ug of ethinyl estradiol combined with 250 mg levonorgestrel. The trial was done in 6 centres in Thailand, India, Zambia, Cuba, The Philippines, and Hungary. There were no significant differences between the two pills at any of 4 follow-up visits at approximately 3, 6, 9 and 12 months, nor in the life-table probability of developing hypertension within one year. These findings are evidence against the hypothesis that it is the estrogen in oral contraceptives which causes their vasopressor effect.

RCT Entities:   Population Interventions Outcomes