In the Women's Health Initiative study there was a relative risk 1.41 at 5.2 years of the development of a stroke (comparing oestrogen plus progestogen arm vs. placebo group) (1) - this meant an increased absolute risk of 8 per 10,000 women per year.
NICE state with respect risk of stroke with HRT (2):
Explain to women that taking oral (but not transdermal) oestrogen is associated with a small increase in the risk of stroke
Current HRT users  | Treatment duration <5 years  | Treatment duration 5-10 years  | >5 years since stopping treatment  | ||
Women on oestrogen alone  | RCT estimate  | 0 (-5 to 10)  | No available data  | No available data  | 1 more (-4 to 9)  | 
Women on oestrogen alone  | Observational estimate  | 3 more (-1 to 8)  | No available data  | No available data  | No available data  | 
Women on oestrogen + progestogen  | RCT estimate  | 6 more (-2 to 21)  | No available data  | No available data  | 4 more (-1 to 13)  | 
Women on oestrogen + progestogen  | Observational estimate  | 4 more (1 to 7)  | No available data  | No available data  | No available data  | 
Reference:
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