A long-term risk-benefit analysis of low-dose aspirin in primary prevention.

BACKGROUND: The long-term risk-benefit effect of occasional and regular use of low-dose aspirin (≤ 100 mg per day) in primary prevention of vascular diseases and cancers was calculated. METHODS: One representative database of 1 000 000 participants from Taiwan's National Health Insurance scheme in 1997-2000 was used. The potential study subjects were those aged 30-95 years, were found not to have been prescribed aspirin before 1 January 2000, but to have first been prescribed low-dose aspirin (≤ 100 mg per day) after that date and were followed up to 31 December 2009. Participants prescribed low-dose aspirin < 20% during the study period were considered occasional users and those prescribed ≥ 80% regular users. After the propensity score matching, rate differences of haemorrhage, ischaemia and cancer between these users were calculated their net clinical risk. RESULTS: A total of 1720 pairs were analysed. During the study period, haemorrhage and ischaemia occurred in 25 (1·45%) and 67 participants (3·90%) in occasional users and 69 (4·01%) and 100 participants (5·81%) in regular users, whereas cancer occurred in 32 participants (1·86%) in occasional users and 26 participants (1·51%) in regular users. The crude and adjusted net clinical risks of low-dose aspirin use between the two frequency of users (≥ 80% vs. < 20%) were 4·12% (95% CI = 2·19%, 6·07%; P < 0·001) and 3·93% (95% CI = 2·01%, 5·84%; P < 0·001). CONCLUSIONS: A long-term regular use of low-dose aspirin might not be better than occasional use in the primary prevention against major vascular diseases and cancer.