In simple words: Taking less of a hallucinogenic drug like LSD or PCP than prescribed or instructed.

Underdosing of unspecified psychodysleptics, such as LSD, PCP, and other hallucinogens, occurs when an individual takes less of the substance than prescribed or instructed. This can be either inadvertently or deliberately done.

Example 1: A patient with a history of hallucinogen use presents to the emergency department reporting that they accidentally took less of their prescribed LSD than instructed. They are experiencing mild withdrawal symptoms., A patient intentionally takes a smaller dose of PCP than usual to try and reduce their tolerance. They experience unexpected and unpleasant effects., A patient is prescribed a hallucinogen for a clinical trial but unintentionally takes less than the prescribed dosage due to confusion about the instructions. They do not experience the intended therapeutic effects.

Documentation should include the type of hallucinogen, the prescribed dose, the dose taken, the method of administration, the time of ingestion, and the signs and symptoms experienced by the patient. Any relevant medical history, including previous substance use, should also be documented.