A hallucination is defined as a sensory perception that occurs without an external stimulus, meaning a person sees, hears, smells, tastes, or feels something that is not truly there. While often associated with mental health conditions or recreational substances, many therapeutic medications commonly prescribed by physicians can induce these altered perceptions as an unintended side effect. These drug-induced experiences result from the medication crossing the blood-brain barrier and interfering with the balance of chemical messengers in the central nervous system. Understanding which drug classes pose this risk can help manage this phenomenon.
Common Classes of Hallucination-Inducing Medications
Several broad categories of prescription and over-the-counter medications carry a risk of causing hallucinations.
Anticholinergic drugs, used to treat conditions like bladder overactivity or motion sickness, are frequent culprits because they block the action of a key neurotransmitter in the brain. Older antihistamines, such as diphenhydramine found in many sleep aids, also possess strong anticholinergic properties that can lead to confusion and visual changes, particularly in older adults.
Dopaminergic medications, primarily used to manage Parkinson’s disease, form another significant class. These drugs, including dopamine agonists and levodopa, increase dopamine activity to control motor symptoms. However, higher dopamine levels are directly linked to the onset of psychosis and visual hallucinations.
Corticosteroids, used for their powerful anti-inflammatory effects, can also cause psychiatric symptoms, including hallucinations, especially at higher doses. Additionally, certain hypnotics and sedatives prescribed for sleep, like the non-benzodiazepine class, have been associated with complex sleep-related behaviors and visual disturbances. Some antibiotics, antidepressants, and anti-epileptic drugs have also been implicated in rare instances of drug-induced hallucinations.
How Drugs Disrupt Brain Chemistry
Medication-induced hallucinations occur when a drug molecule mimics, blocks, or alters the concentration of chemical signals used by brain cells. The two most commonly implicated neurotransmitter systems are dopamine and acetylcholine.
Dopaminergic drugs overstimulate dopamine receptors, particularly in pathways governing reality perception, leading to false sensory input. Anticholinergic medications cause hallucinations by blocking acetylcholine, a messenger involved in learning, memory, and attention. Suppressed acetylcholine signaling impairs the brain’s ability to process sensory information, often leading to disorganized or complex visual changes.
Other medications can interfere with serotonin signaling, particularly the 5HT2A receptor, a mechanism similar to classic psychedelic substances. Corticosteroids can dysregulate the entire neurochemical environment by affecting the hypothalamic-pituitary-adrenal (HPA) axis. This influence, in turn, affects the levels of multiple neurotransmitters, including dopamine and serotonin.
Recognizing the Difference Between Hallucination and Delirium
It is important to distinguish a true hallucination from the broader state of delirium, as both can be triggered by medication but are medically distinct.
A true hallucination is a specific sensory perception that the patient may recognize as unreal, such as seeing a detailed image of a person who is not present. The person’s overall level of attention and awareness often remains relatively intact, a state sometimes referred to as “retained insight.”
Delirium is a more global state of acute confusion marked by sudden onset and a fluctuating level of consciousness and attention. A person experiencing delirium will have disorganized thinking and difficulty concentrating. While hallucinations may be a component of delirium, the defining features are the profound loss of cognitive clarity and the inability to focus or sustain attention.
Steps to Take When Experiencing Drug-Related Visual Changes
If you begin to experience visual changes or hallucinations while on a new or adjusted medication, contact the prescribing physician immediately. Never abruptly stop taking a prescribed medication without explicit medical guidance, as this can lead to dangerous withdrawal symptoms or a flare-up of the underlying condition.
When speaking with the healthcare provider, describe the exact nature of the experience, including what was seen, heard, or felt, and when the symptoms started in relation to the dose. The physician will assess whether the medication is the likely cause and may suggest lowering the dosage, switching to an alternative drug, or safely stopping the medication. Hallucinations are often dose-dependent and typically resolve quickly once the drug is adjusted or discontinued.