Drugs that blockade the 5-htp2-A stop LSD trips fairly quickly. Risperidone is one example. I have a belief that its not good to abruptly stop a trip except when required by an emergency. I'm sure Psychedelic Drugs has dealt a lot with question and might have a megathread to merge this into. Oh be aware that you want to be aware of the whole effects profile for any drug you might use to stop a trip.
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