With both of these drugs you never know how you're going to react, so with acid I would definitely take no more than 1 hit your first time.
If it does nothing after a couple hours, MAYBE take another but I wouldn't. First time I took acid I took a black gelcap, and an hour and a half later, I didn't feel anything so my friend gave me 2 more, thinking it was weak. Well, it sure as hell WASN'T weak, just a little slow. Within 10 minutes I was so completely fried, I couldn't even talk. I just stared into a cup of water for a couple hours. It was WAY too intense for my first time, because I didn't realize how deep an acid trip delves into your psyche. Make sure you have trustworthy people around you, in case you're not feelin so hot. I had good people around me & fortunately pulled thru with only a minor episode, but remember mirrors aren't always a good thing to have around, but some bomb chronic is essential, also a cozy blanket & maybe even a bear (sorry, i still sleep with a teddy bear @ almost 25

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As for shrooms, I'd do a couple caps/stems, just in case you have a sensitive stomach, to keep yourself from throwing up. Remember with shrooms, you're basically "poisoning" yourself, and the hallucinations are a result of it ~ so too many can make you pretty sick to your stomach. About an eighth of shrooms should suffice @ maximum for your first time.
Happy Trails & hope you have a nice safe trip