For most people depressants and stimulants work as advertised, for some they have the opposite effect. A depressant like an anti-histamine or GABA medication will stimulate them and wire them up. For some people stimulants like cocaine make them feel relaxed and sleepy.
Is anything known about the neurology of why this happens? I know for people with ADD stimulants can have a paradoxical effect, I’ve heard because for those people stimulants can take neurotransmitters that are too low and raise them to normal levels (whereas for most people they have normal levels risen to high levels from the drug. But that still doesn’t explain why some people fall asleep when using cocaine.
But I still don’t get why benadryl or xanax can cause some people to become hyper and wired.