This non-authoritative article at Wikipedia gives a short description about Viagra, its history, method of action, contraindications and side effects, et cetera ad nauseam.
Basically, sildenafil works by increasing blood flow to the penis. It will not give perma-erections (which are potentially damaging anyhow). Along with the side effects listed in the article, some people here have reported that Viagra curiously makes ejaculation more difficult.
Good luck and please consult the proper healthcare practitioner before using this prescription-only pharmaceutical.
I think I'd go with Steph and not try it during the weekend. Just as one wouldn't try a race car the day of the race. Could work, but could go wrong just the same way. I'm not too keen on any new drugs, specially if not needed, but that's me.
My advice would be just to have half a tablet the first time. If you are taking it as an erection enhancer rather than a necessity for a dysfunction then half a tablet should be quite sufficient in any case.
When (if) you take it you'll find that something that would usually make you only half erect will now have you standing firmly to attention - as has been said though, in the absence of sexual stimulation of some form or another you won't be hard.
Let me save him the journey. Your doctor will tell you not to take it.
We use Cialis and it last practically all weekend. The first 2 times he used it he had a headache and some muscle aches, but now no problems at all. I've tried it too, but no headache and couldn't tell if it did anything for moi. He tried Viagra, but nothing. We use it for swing situations, and at first he took a half, but then moved it on up to a whole pill. We find it is very helpful and handy.
The truth is just an excuse for a lack of imagination.
I was looking in to trying one of those products. I don't really need it, but with work and stuff I've been tired and stressed and was worried about my performance on special occasions (anniversary etc...) and was thinking of taking one to make sure I could perform when needed. For everyday sex, I'm not as worried since she'd understand if I'm too tired and just want to sit on the couch or go to sleep. Any suggestions on where I can pick some of that stuff up without a doctor's note? Let me clarify, any safe trustworthy place.
It really depends where you live. In most of the world it is quite legal to buy such drugs over the internet (I can provide you with addresses if you wish) but in some of the more highly regulated nations such as Iran, North Korea and the USA (with its monstrous FDA) there is much less scope given for adults to make their own pharmacologically based decisions.