The effects of guava leaf extract on the bleeding time and the three main mechanisms of haemostasis: vasoconstriction, platelet
aggregation and blood coagulation, were investigated. The water extract of guava leaves did not shorten bleeding times in rats.
Guava leaf extract potentiated the vascular muscle contraction induced in rabbits by phenylephrine, and when given alone it
stimulated human platelet aggregation in vitro in a dose-dependent manner. On the other hand, it significantly prolonged blood
coagulation; activated partial thromboplastin time (APTT) test (p < 0.05). The higher the concentration of the extract, the longer
APTT was observed. Thus, a water extract of guava leaves showed ambiguous effects on the haemostatic system. Guava leaf extract
did not affect bleeding times, it stimulated vasoconstriction and platelet aggregation but it inhibited blood coagulation.
Therefore, guava leaf extract is not recommended as a haemostatic agent.