Hallucinations: What Causes Them?
- Peter M. Hartmann, MD, DLFAPA
- May 27
- 4 min read
There are some surprising reasons for hallucinating, and some are even normal.
Key points
Hallucinations can be caused by mental and general medical conditions. They can also be normal.
Anyone with a new onset of hallucinations should be evaluated in a timely manner by a physician.
Children and teenagers can have normal hallucinations, but sometimes they are due to a disorder.
Hallucinations are unreal sensory experiences, such as hearing or seeing something that is not there. Any of our five senses (vision, hearing, taste, smell, touch) can be involved.
Most often, when we learn someone is hallucinating, we think about psychosis, such as schizophrenia. Hallucinations can also occur in people who have bipolar disorder with psychosis or major depressive disorder with psychosis.
While these mental disorders are common causes of hallucinations, there are numerous general medical causes as well. For example, people with a variety of neurological illnesses may hallucinate. Those illnesses include migraine headaches, Parkinsonism, some dementias, delirium, brain tumors, and others.
Brain tumors in the frontal lobe often present with a personality change. Another early symptom can be hallucinations of smelling burnt rubber. This is a good example of a hallucination related to the sense of smell.
One fascinating cause of visual hallucinations can occur when someone has a severe disease of both retinas in their eyes. For example, there was a patient who had a viral infection in each of his retinas. He reported seeing tiny people and small animals playing and running around his hospital room.
Of course, he was having a visual hallucination. The virus stimulated his retinas, which sent signals to the occipital lobe in the back of his brain, where vision processing occurs. His brain interpreted the signals as real images.
His general medical doctor worried that he was psychotic. A psychiatric consultant determined that the patient was not psychotic but hallucinated because of his retinal infection. The patient was reassured that his visions were not due to psychosis but were a reaction to his eye infection. No treatment was needed.
Substance use disorders are common sources of hallucinations. These substances include alcohol (especially during severe withdrawal known as delirium tremens), amphetamines, and hallucinatory drugs such as LSD and PCP. They can cause a variety of hallucinations, especially visual ("pink elephants"), auditory, and tactile. An example of a tactile hallucination is a sensation of insects crawling under the skin or of internal organs moving around. It is frightening for the patient who believes that it is really happening.
Hallucinations can occur in patients who are taking certain medications as a side effect. Examples include some antihistamines, opiates, SSRI-type antidepressants (e.g., fluoxetine), steroids like prednisone, sleeping pills, and many others.
Because there are more general medical causes of hallucinations than mental health disorders, anyone experiencing hallucinations for the first time should see a medical doctor soon. The patient may suffer great harm if the underlying medical condition is not diagnosed and appropriately treated.
Sometimes, hallucinations may occur in people who don't have a mental health or general medical cause. These hallucinations are normal. One common example can happen after the death of a loved one, such as a beloved spouse. The bereaved spouse may "see" their deceased spouse standing at the foot of their bed at night.
These hallucinations are common and normal. However, people who are unaware that this is normal may be frightened and wonder, "Am I losing my mind?" Reassurance from a physician or mental health professional is usually all that is needed.
Another cause of normal hallucinations is related to sleep. These individuals usually have visual hallucinations when they are falling asleep. It occurs during the transition from wakefulness to their first dream. We dream about five times each night when rapid eye movements take place.
These hallucinations are called hypnagogic hallucinations. People may also hallucinate while they are waking from sleep. These are known as hypnopompic hallucinations. They can be potent enough that the person believes that it really happened.
For example, a person who wakes up while having a vivid dream of being kidnapped by aliens and experimented on may think that really happened. This can explain what was going on when someone reports being roused from sleep by aliens.
Children and teenagers can have normal hallucinations (Naijer, 2019). They are typically self-limited and are not associated with any other symptom of mental or general medical illness. They are thought to be part of normal development. No treatment is needed.
Despite normal hallucinations in children and teens, there is some evidence that a few of these children and teens have an increased risk of suicide. This may be because some of them have a disorder that is not fully manifested. It is reasonable to monitor these children and teens.
In summary, hallucinations can be caused by mental health and general medical disorders. In some cases, the hallucinations may be normal. Because hallucinations are caused more often by general medical disorders than mental health disorders, everyone with new-onset hallucinations should be promptly evaluated by a physician, such as a psychiatrist.
