Hallucination

Hallucination is a perception that arises without any corresponding external stimulus and is experienced as genuinely present — the person having it cannot distinguish it from ordinary sensory input.

This is distinct from the perceptual distortions and pseudohallucinations that classic psychedelic experiences more commonly involve. A pseudohallucination is vivid and sometimes elaborate, but the person experiencing it retains awareness that it is not real. A hallucination is believed.

The distinction carries practical weight in harm reduction. True hallucinations are more associated with deliriants such as atropine and scopolamine, high-dose stimulant psychosis, severe withdrawal from alcohol or certain depressants, and dissociatives at extreme doses — contexts where other risks are also elevated.

How it is done

Recognising whether an experience constitutes a hallucination or a pseudohallucination comes down to a single question: does the person understand, in the moment, that what they are perceiving is not external reality?

Someone who sees elaborate visual phenomena during a psychedelic experience and knows they are drug-induced is not hallucinating in the clinical sense. Someone who believes a figure is present in the room when no one is there, or who responds to voices others cannot hear, is.

This recognition is often more accessible to a sober observer — a sitter or companion — than to the person in the experience. A person who is genuinely hallucinating will typically respond to the content of the hallucination as if it were real: reaching for things that are not there, acting on what they believe they see, or becoming frightened of something no one else can perceive.

When it matters

True hallucinations become an urgent concern when they appear alongside signs of a medical emergency: significant confusion or disorientation, inability to hold a conversation, elevated heart rate or body temperature, or visible physical distress. These signs together suggest delirium rather than a predictable substance effect, and delirium can deteriorate rapidly.

Severe alcohol and benzodiazepine withdrawal are among the more dangerous contexts for hallucinations — a person hallucinating during withdrawal may be approaching seizures and warrants medical evaluation regardless of whether they appear otherwise stable.

A person experiencing true hallucinations should not be left alone. Whether to involve emergency services depends on the full picture: the substance context, how long the experience has lasted, the person's physical condition, and whether they can be kept oriented and physically safe in the interim.

What it cannot tell you

Knowing that someone is experiencing true hallucinations does not identify the cause. A hallucinating person may be in the acute phase of a delirant, in stimulant-induced psychosis, in withdrawal from a depressant, or in a psychiatric crisis unrelated to substance use. The presentation can look similar across all of these.

Hallucinations also cannot rule out co-occurring dangers. Delirium — which can include hallucinations — is typically accompanied by other signs: disorientation, elevated heart rate, difficulty tracking conversation. The absence of obvious physical distress does not establish that a situation is not medical.

A reassuring answer from the person does not establish that they understand their situation accurately. Loss of insight — the inability to recognise one's own perceptions as unreal — is part of what defines a true hallucination, not a feature that can simply be asked about.