Hypnosis is a procedure that opens people to the power of suggestion. A hypnotist puts a subject in an altered state by encouraging relaxation and sleepiness and often describing the sorts of physical sensations a subject should be feeling. Once a subject is in the altered state, he or she may act, perceive, think, or feel according to the hypnotist’s suggestions. Not everyone can be hypnotized, and some people are more hypnotizable than others. The following chart shows what hypnosis can and can’t do.

If hypnotized people are instructed to forget what happened during hypnosis, they later claim to have no memory of it. This phenomenon is called posthypnotic amnesia.

A hypnotic state isn’t sleep—brain waves, for example, do not reliably change during hypnosis as they do during sleep. Researchers don’t even agree that hypnosis is an altered state of consciousness. Researchers propose two main theories about hypnosis:

Meditation is the practice of focusing attention. People meditate to enhance awareness and gain more control of physical and mental processes. Techniques used in meditation vary and include activities such as repetitive chanting and breathing exercises.

Meditative states are associated with an increase in alpha and theta brain waves, and physical indicators of relaxation such as slowed pulse and breathing. Some researchers have found that meditation has long-term effects such as improving physical and mental health and reducing stress. However, researchers disagree about whether meditative states are unique states of consciousness. Some researchers believe relaxation techniques can produce the same kind of state produced by meditation.

Psychoactive drugs, as opposed to medicinal drugs, have psychological effects, meaning that they change sensory experience, perception, mood, thinking, and behavior. Psychoactive drugs are sometimes called recreational drugs, though some have legitimate medical uses.