The effect of coffee drinking on platelet reactivity was studied in 12 healthy subjects. Plasma beta‐thromboglobulin concentration was determined before and one hour after administration of 100 mg of caffeine, corresponding to one cup of coffee. Mean values were 47.0±19.3 and 179.3±85.5 ng/ml before and after caffeine administration respectively. The increase, 298±150%, is highly significant (p<0.001).

The authors previously reported an increase in platelet aggregration in the days after coronary angiography, accompanied at times by worrying cardiovascular disorders (ventricular fibrillation in one case, death in two others). In the present study, ten patients received a platelet antiaggregating drug (ticlopidin) 5 days before their coronary angiography. No significant changes were detected in the test for circulating platelet aggregates (CPA test) in these patients.