Ouch.
Oh yeah, I know this has probably been already stated, but pot decreases muscle. I've actually noticed it, too. A group of my friends do it daily, and their arms have absolutely no muscle value.
If you do it once in a while, it's not bad. Every day can actually cause body changes though.
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So weight lift or do something after doing so, but you are correct, once in a while it can't be that harmful unless you're so high that you jump in front of a train, but we're not going there.