Hallucinations are ‘tricks’ played on the senses on the body, making them sense things that are not there. While many people associate hallucinations with ‘seeing things’, there are also many other types of hallucination which can involve hearing, smelling, tasting and feeling things that are not there. There are many things that can cause a hallucination and working out the cause is often difficult to achieve in a GP consultation so referral to a specialist is sometimes needed.

What are Hallucinations?

Hallucinations are false sensory perceptions, or ‘sensing’ things that are not there. This does not mean that they just have a ‘feeling’ that something is there, but rather than the usual senses we use to interpret the world, such as sight, hearing, taste, touch and small, are malfunctioning in some way. The most common type of hallucination is a visual hallucination where people see things that are not there. These visual hallucinations can be whole objects such as people (known as ‘formed’ hallucinations) or just flashes of light and colours (known as ‘unformed’ images). Other types of hallucinations include:

  • Auditory: false perceptions of sound, usually voices but occasionally music and other noises; most often occurs in psychiatric disorders.
  • Olfactory: false perceptions of smell
  • Gustatory: false perceptions of taste
  • Tactile: false perception of touch or other sensation, as from an amputated limb.

Some people can have quite vivid hallucinations just before they fall asleep at night as well as in the morning upon waking. These are known as hypnagogic and hypnopompic hallucinations and most people will have these at some point in their life. They are so common that they are considered almost normal and are not dangerous or caused by any medical problem but is especially common in people suffering from narcolepsy.

Why Do People Hallucinate?

People are still a little uncertain as to how hallucinations are formed and why they occur, but there are a few theories that seem to each play a part. The most common theories involve chemicals in the brain known as serotonin and dopamine. These chemicals are usually present in the brain to transmit signals from one brain cell to another and it is thought that in hallucinations some of these might be found in high levels, or in the wrong place. Other theories include that hallucinations are the brain interpreting normal visual signals wrong, or that the signals sent to the brain are faulty to begin with.

What Causes Hallucinations?

There are lots of conditions that cause hallucinations, of which most are medical but some are psychiatric. Some major causes include:

When Should I See a Doctor About Hallucinations?

If you ever begin to have a hallucination, then it is always best to seek medical attention. Some people may be afraid that the doctor will think they are ‘going mad’ if they present with hallucinations, but as can be seen above there are many very serious medical conditions that can account for hallucinations and they need to be looked into. If you have any auditory hallucinations such as hearing voices when no one is around, or the television making noise even when it is off, it is important that you seek medical attention immediately. If you ever think of harming yourself or harming others it is also vitally important that you seek help as soon as possible.

What Will the Doctor Ask and Do?

Firstly, the doctor will probably want to get a very clear idea about exactly what the hallucinations involve, when they started and what type they are. They may ask a lot of questions that seem quite basic or even silly to you, but these are important questions that need to be asked to make sure that there is nothing more sinister going on. They may ask you to fill in a form or do a small test to check your memory. They will also want to know if there were any other symptoms around the time of the hallucinations; having someone with you who was there during the period of hallucinations can help give this information. They may also ask you a lot of questions about your health in the past as well as asking about any medications that you may be on. While it may seem odd, the doctor will probably ask you about the amount of alcohol that you drink or usually drink as well as if you use any more illicit drugs.

This forms part of every normal assessment and should not be taken as an accusation. The doctor may also ask some questions about your awareness that the hallucinations are not real. They may also ask questions about your mood, as serious depression can sometimes manifest as hallucinations. The doctor will then want to examine you to see if there are any signs of infection, liver problems, kidney problems or thyroid problems. While there are many tests that can be run in a patient with hallucinations, going through them all here is not very practical as it will very much depend on what the doctor thinks the cause of the hallucinations is. In some cases a general practitioner may refer to a specialist such as a neurologist, psychiatrist or geriatrician for assistance with regards to a patient with hallucinations. There they will ask further questions with regards to the hallucinations to work out the exact cause.

Is There Treatment for Hallucinations?

Treating hallucinations all depends on what the condition is that is causing the hallucinations in the first place and so it is impossible to give a universal treatment. For information about the treatments for conditions that can cause hallucinations, click on the links above.


  1. Kapur, S. Psychosis as a state of aberrant salience: a framework linking biology, phenomenology, and pharmacology in schizophrenia. American Journal of Psychiatry, 2003, 160(1): 13-23.
  2. Manford M, Andermann F. Complex visual hallucinations. Clinical and Neurobiological insights. Brain, 1998, 121(10): 1819-1840.
  3. Murtagh, J. General Practice (Third Edition). Sydney, McGraw-Hill, 2005.
  4. Sadock B, Sadock J. Pocket Handbook of Clinical Psychiatry (Fourth Edition). Philidelphia, Lippincott Williams and Wilkins, 2005.

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