perfectly safe. All alone in a lab somewhere, anyways. The effects it has on one's psyche however, are not always ideal. If you have any sort of issues discerning reality or your place in it, manifesting in ways that might be dangerous while sober (deathwish, depression, mild-megolomania, chemical imbalance, rage issues, that sort of thing) you can go straight out loopy and hurt yourself or someone else before it wears off.
I'd say that's the most dangerous thing about it. You cannot, under any circumstances or scenarios, or by using any amount of coffee, speed or other chemical stimulants or methods, ever get an acid trip to stop. It will continue until it is done with you. And that might be 24 hours. No shit.
I'd also suggest not going anywhere whatsoever near an automobile or roadway in any fashion. If you do, even if you make it from point A to point B unscathed, you will be regretting it. Especially if you end up somewhere you can't spend the rest of your time and have to turn around and go back home. That really sucks.
Weed becomes useless. You will wonder afterward why you wasted it if you smoke it when tripping. I'm not sure about anything else, since that's all I was ever really into. Beer is good, though. It almost mellows you out (very little) and the constantly having to go to the bathroom gives you a mild distraction from the pervasive feeling of your mind melting like old cheese in a microwave and the contorting freakshow the world around you will appear to become. Try not to stare into the mirror too much, and for the love of god, don't shave anything! Wait until tomorrow!
But, it isn't addictive, unless you are allready a fucking nutjob, and even then I doubt it. It's sort of like hooking a turbo-charger up to your brain-stem, standing in a puddle and putting your finger into a light socket, and picking your nose with lightning all at the same time. It doesn't mess you up like booze, or get you high like other drugs, it rewires your mind completely for a few hours. And if you loose the battle to maintain who you were before you ate that little droplet of stuff, you might end up batshit loco indeed.
Or so I hear anyways, I've never done it.
Just say no, kids.