Can caffeine act as viagra Recently I studied that cAMP which is a 2° messenger can cause various physiolocal changes under the action of proper hormones. Now cAMP is degraded by phosphodiesterase and this ceases the actions. Viagra drugs like sildenafil are phophodiesterase inhibitors and therefore prolong cAMP action. Also caffeine inhibits phosphodiesterase and therefore it should cause a similar phenomenon. But does it actually happen? Or some other mechanism stop it from happening. What are those mechanisms?

Not much luck there. Although caffeine, sildenafil and cGMP share a basic ring structure, the specificity and potency of caffeine for PDE5 is rather underwhelming:

> On the basis of comparative IC50 values, the potency of sildenafil is about 1 million times higher than that of caffeine (Corbin and Francis, 1999).