Shrooms

You trip via a pretty simple mechanism. Your brain is full of the neurotransmitter seretonin. Structurally the seretonin molecule is similar to pshychedelics like psiolcybin and LSD. So similar in fact that your brain mistakes the psychedelic molecules for its own seretonin which obviously causes a lot of [harmless] changes in your brain chemistry, which then affects your perception of the world. The changes in brain chemistry are also temporary, with no evidence to show long term effects.

Many drugs are involved with seretonin. THC binds to your seretonin molecules, while MDMA changes your seretonin receptors.

Other drugs work via different interactions. Cocaine interferes with the neurotransmitter dopamine, whil the opiates such as heroine are very similar in structure to your endorphins.

i seconed this post^^^^