In hallucinations you perceive things that are not there. It really is an observation that seems to be real. For example, you may hear sounds (auditory hallucinations) or see something or someone (visual hallucination). This is in contrast to a change in sensory perception where normal perception is distorted. Think of a person’s voice that sounds higher or lower or a face that seems to have a big nose.

Hallucinations can be both desirable effects (with psychedelics) and unwanted side effects (with high doses of MDMA, or with being awake for too long).