ive had a lot of caffeine and im feeling really jittery and i know i'll have trouble sleeping tonight. is there anything i can do to like cancel out all the caffeine ive had

I drink too much caffeine quite a lot.. usually I'll just drink a lot of water, or go for a run to try and get it out of my system.. I don't know if there's a surefire way though.

Chamomile tea will bring you down.

smoking helps speed up caffeine break down, so have a few fags

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since you must completely metabolize the caffeine to "come down", it may help for you to do some vigorous exercise. the half life of caffeine in your body is about 4 hours, meaning that 4 hours after your coffee about half of the caffeine has been metabolized. that's why you should try to avoid drinking caffeine in the afternoon or evening.