Type of hormone replacement therapy and risk of venous thromboembolism

The results of randomised studies have been fairly consistent in finding an increased risk of venous thromboembolism with oral hormone replacement therapy. The accompanying systematic review by Canonico and colleagues finds similar results.1 The review combined data from both randomised and observational studies and found that the risk of venous thromboembolism doubled with oral hormone replacement therapy compared with placebo (pooled odds ratio 2.4, 95% confidence interval 1.9 to 3.0).

Results from the observational studies alone were then pooled to assess the risk of venous thromboembolism from different types of hormone replacement therapy and duration of use. No significant difference was seen between combined therapy and oestrogen only (2.6 v 2.2; P=0.45). Risk of venous thromboembolism was significantly higher during the first year of treatment with oral oestrogen (4.0 for a duration of less than one year; 2.1 for more than one year), and past treatment was not associated with an increased risk (1.2, 0.9 to 1.7). The results echo …