Viagra in NOT an aphrodisiac. It does absolutely nothing for sex "drive" or "desire". Its only "sexual" mechasnism is that it increases blood flow to the genitalia in men that have erectile disfunction. Not even spontaneous erections either, the male must be sexually aroused first. So if there is no desire and no one to stimulate the ole' penis, then there will be no woody even if you did take viagra.
Now that being said, there has been anecdotal evidence that it may allow more blood flow to the clitoral area in females thus increasing sensitivity when stimulated.....but again, Viagra does NOTHING for sexual appetite.