Sex, and things close to it, have a proven effect on the metahuman metabolism.  Namely, that it accelerates it beyond normal levels.  Now, while this is useful on one hand (some studies say a good round or three of sex is like exercising for an hour), it also has its drawbacks - namely, that if drugs are administered to the individual while under that accelerated metabolism, the drugs are absorbed and the effects felt more quickly...which was<em>exactly</em>what Akiko had planned, and<em>precisely</em>what happened.