>>405227
SSRI's slow down the uptake of serotonin in the brain, causing it to build up and last longer in the brain.
Lsd dumps serotonin into the brain and floods the receptors causing the "trip" (among other things happening). Its been shown that people having a psychotic break have increased levels of serotonin.
LSD and SSRI's are similar in the sense that heroin and cocaine are similar. One dumps dopamine into the brain the other slows down its uptake and makes each molecule last longer.