Viagra doesn't give you unpreventable hard ons, it improves circulation and thus makes them easier. And tans, you didn't seriously have a hard on for 10 hours without respite? 10 hours with it up and down like a yo-yo perhaps!
(Anything over 4 hours without becoming flaccid and you are at serious risk of clotting, damaging the blood vessels on a permanent basis and being unable to become erect ever again. It's even possible to cause gangrene and need your cock removing in extreme cases.)
I don't know why people sprinkle it in pints to be honest, often little bits of it remain floating and it changes the taste very obviously. It's very bitter and the effect it has on an unstimulated person, if taken in the correct amounts, is negligible. Unless of course you give him too much in which case you can cause the previously mentioned problems. Spike his drinks with LSD, that would be far funnier.
