I have some lsd that's been sitting in a plastic bag for a year and a half. Any know how long it keeps?

If the bag was airtight and stored in a cold dark place it shouldn't have lost much potency.
You can just send some to me and I can bioassay it for you

My bet would be its bad, i had some awesome blotter stored in a cellophane kept in a dark watch box, 2 years later it was just paper...since then i've read to keep it in tin foil and in the freezer this hypothetically eliminates the expiration date...hopefully you have better luck than i but i wouldn't hold my breath...

I guess it depends a lot on the initial amount of lsd, a 200 mic could obviously be stored much longer than a 50 mic one.

lsd is pretty notoriously unstable. I misplaced a sheet of acid once (I know..) I found it almost a year later, I had it wrapped in foil in a book like a bookmark. It wasn't completely inactive, but I ended up taking like 60 hits of it to get where I wanted to be..

My guess is the paper is either inactive or close to inactive.

I have had good luck with keeping it wrapped in foil in the freezer for over 2 years though.

One way to find out