A hallucination is a sensory perception that occurs without an external stimulus, meaning a person perceives something that is not actually present. These experiences are distinct from illusions, which are misinterpretations of an actual external stimulus, or vivid dreams. While often associated with mental health conditions, hallucinations are also a recognized side effect of numerous therapeutic medications. The likelihood of drug-induced hallucinations often increases with age, higher dosages, and the use of multiple medications simultaneously.
The Mechanism of Drug-Induced Hallucinations
Medications disrupt the brain’s normal sensory processing by interfering with neurotransmitters. The central nervous system relies on a delicate balance of these chemicals, and altering their activity can lead to sensory misinterpretation. This effect is often dose-related and resolves once the causative medication is stopped or the dosage is lowered.
One primary pathway involves the neurotransmitter dopamine, specifically its activity at the D2 receptors. Medications that increase dopamine transmission, such as those used to treat Parkinson’s disease, can overstimulate these pathways, inducing psychosis and hallucinations. A disruption in the activity of acetylcholine, which is important for cognitive function and memory, is also a common cause.
Drugs that block acetylcholine are known as anticholinergics. Their action can lead to confusion, delirium, and vivid hallucinations. The serotonin system is also implicated, as certain hallucinogenic drugs act as agonists at the 5-HT2A serotonin receptors. Medications that indirectly increase serotonin availability, such as some antidepressants, have also been reported to cause hallucinations.
Common Prescription Drug Classes
The risk of hallucinations is not limited to psychiatric medications. Several widely used prescription drug classes can affect the central nervous system, leading to sensory disturbances. These effects are often more likely to occur in older individuals who may be more sensitive to changes in brain chemistry.
Dopamine Agonists
Dopamine agonists are frequently prescribed for conditions like Parkinson’s disease and Restless Legs Syndrome. These drugs mimic dopamine to manage motor symptoms caused by low dopamine levels. The resulting overstimulation of dopamine receptors can trigger visual hallucinations, ranging from fleeting images to complex scenes.
Increasing dopamine can inadvertently lead to an imbalance in the brain’s reward and sensory pathways. This side effect is a known complication of Parkinson’s disease treatment, as the underlying condition itself can also predispose a person to hallucinations. Ropinirole and pramipexole are examples of dopamine agonists where this risk is documented.
Sedative-Hypnotics
Medications prescribed for insomnia, often called “Z-drugs,” have been linked to unusual sleep-related experiences. Nonbenzodiazepine sedative-hypnotics, such as zolpidem, can cause complex sleep behaviors and sensory disturbances. Hallucinations may occur as a person is falling asleep (hypnagogic) or waking up (hypnopompic).
These occurrences are rare but are more likely with higher doses or when the medication is taken without allowing for a full night’s sleep. The effects stem from the drugs’ interaction with GABA receptors, which regulate central nervous system depression, leading to altered states of consciousness.
Corticosteroids
Corticosteroids, such as prednisone, are anti-inflammatory and immunosuppressive agents used to treat conditions ranging from asthma to autoimmune disorders. High-dose or prolonged use carries a risk of inducing steroid-induced psychosis, which can include hallucinations. Symptom onset is most likely within the first few days of starting treatment or following a significant dose increase. The mechanism is thought to involve the broad influence of corticosteroids on various neurotransmitter systems.
Anticholinergics and Antispasmodics
Anticholinergic medications are used for diverse purposes, including treating overactive bladder, muscle spasms, and gastrointestinal issues. These drugs block the action of acetylcholine, and this blockage can profoundly affect brain function. The resulting disruption of cholinergic signaling can precipitate confusion, delirium, and vivid hallucinations.
First-generation antihistamines also possess strong anticholinergic properties, allowing them to cross the blood-brain barrier and affect cognitive processing. This mechanism explains why many different drug classes that share this anticholinergic action carry a similar risk of causing sensory disturbances.
Non-Prescription and Over-the-Counter Agents
Hallucinations are not exclusive to prescription medications. Several readily available over-the-counter (OTC) agents can induce these effects, particularly when taken at high doses or misused. Understanding their potential for central nervous system effects is important due to the accessibility of these products.
Antihistamines
Older-generation antihistamines, such as diphenhydramine, are commonly used for allergy relief or as sleep aids. These medications have significant anticholinergic properties, allowing them to enter the brain and interfere with cognitive function. In doses far exceeding the therapeutic recommendation, they can cause a toxic state leading to delirium and visual hallucinations.
The risk is amplified in older adults, who may experience these effects even at standard dosages due to increased sensitivity and reduced drug clearance. Newer, non-drowsy antihistamines are less likely to cause these effects because they have fewer anticholinergic properties and do not cross the blood-brain barrier as readily.
Cough Suppressants
Dextromethorphan (DXM), a common active ingredient in many OTC cough and cold preparations, can cause hallucinations when ingested in large quantities. When taken significantly above the recommended therapeutic dose, DXM acts on several central nervous system receptors, including NMDA receptors, leading to dissociative effects.
This misuse can result in sensory distortions, including visual and auditory hallucinations, along with feelings of detachment from reality. The potential for misuse is a recognized public health concern because these cough suppressants are easily obtained.
Actions to Take When Experiencing Hallucinations
If a person experiences hallucinations and suspects a medication is the cause, the first step is to seek immediate medical consultation with the prescribing healthcare provider. It is important not to abruptly stop taking any prescription medication without a doctor’s guidance, as sudden discontinuation can lead to severe withdrawal symptoms or a dangerous exacerbation of the underlying medical condition.
The medical evaluation involves a thorough assessment to rule out other possible causes, such as infection, dehydration, or an underlying medical condition, which can also trigger delirium and hallucinations. The clinician will need detailed information on the timing, frequency, and specific nature of the hallucinations to determine the connection to the medication.
Treatment involves a careful adjustment of the medication regimen, which may include lowering the current dosage or switching to an alternative drug class. The healthcare team may also advise monitoring and documenting the events, which provides essential information for safely adjusting the treatment plan.