LSD causes its effects mainly by activating one type of receptor for serotonin. Because serotonin has a role in many important functions, LSD use can have many effects. These may include sleeplessness, trembling, and raised heart rate and blood pressure.
LSD users may feel several emotions at once (including extreme terror), and their senses may seem to get crossed—giving the feeling of hearing colors and seeing sounds.
Even a tiny speck of LSD can trigger these effects. And LSD has an unusual “echo”: many users have flashbacks—sudden repetitions of their LSD experiences—days or months after they stop using the drug.
Have your perceptions been
Hallucinogens can change the way you see things. The experience is a little like looking at the optical illusion above.