Well, I should say that that is a really dangerous thing to do - spiking someone with Viagra. But anyways, Viagra only works when you are sexually stimiulated... and if that is the case, completing a sexual act, whether it be masturbation or sex (vaginal, oral or anal) will relieve the blood flow and relax the penis to its normal state. Viagra is only in the system for about 4-5 hours so, deal with it till then. But you cannot counteract the medication by voodoo or anything.