Several commonly used therapeutic drugs and medications, and some recreational drugs, are known to produce memory disturbances. Temporal association with the drugs is the only characteristic feature of drug-induced amnesia. Benzodiazepines are the best-known examples. Although, as a class, benzodiazepines act rapidly and are well tolerated, their use continues to be associated with memory impairment. Anticholinergics impair memory retrieval, especially free recall. Drugs with anticholinergic activity also contribute to verbal memory deficits. Various pathomechanisms of drug-induced memory deficits are discussed in this article. Discontinuation of the medication causing memory disturbance is usually enough, and the patient may recover spontaneously. Memory training exercises may accelerate the recovery.
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• Several drugs, both therapeutic and recreational, can produce memory disturbances.
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• Several mechanisms are involved in drug-induced memory impairment.
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• Drug-induced amnesia is not necessarily related to the sedating effects of drugs.
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• Discontinuation of the medication causing memory disturbance is usually enough for recovery.
Historical note and terminology
Several commonly used therapeutic drugs and medications, and some recreational drugs, are known to produce memory disturbances, as is exposure to industrial chemicals. The focus of this article is on medication-induced memory disturbances, but studies of drugs of abuse, both experimental and clinical, also shed light on the pathomechanisms of drug-induced memory loss.
The first mention of a therapeutic drug-induced dementia was after the introduction of synthetic drugs for the treatment of Parkinson disease (34).
The frequently used term “cognitive impairment” refers to disturbances of information processing, which covers the acquisition, storage, retrieval, and use of information. According to the "working memory" model, the allocation of limited resources available for information processing is under the control of the central executive. Working memory corresponds to the set of things we are attending to at any given moment. Thus, attention and memory are processes that operate together, and drugs affecting attention would be expected to impair memory as well. Cognitive disturbances include delirium, disturbances of memory, intellect, and behavior. Various terms referring to memory disorders in this article are:
Amnesia. Usually refers to a pathological loss of memory. Memory is disturbed in several conditions often secondary to disorders of attention. Isolated memory loss, also referred to as an amnestic syndrome, is also seen as an adverse reaction to drugs.
Retrograde amnesia. Refers to difficulty in recalling events that have occurred in the premorbid period. It is usually present in amnestic state or syndrome and affects individuals for a limited period.
Anterograde amnesia. Implies difficulty in registering new information (learning ability).
Transient global amnesia. A clinical syndrome characterized by abrupt onset of severe anterograde amnesia from which the patient usually recovers within hours except for the memory gap for the duration of the attack.
Loss of episodic memory, ie, a person’s unique memory of a specific event, can be affected by neurologic disorders such as a traumatic brain injury, hydrocephalus, brain tumors, and metabolic conditions such as vitamin B1 deficiency.
Fugue. An episode during which a person assumes a new identity and has no memory of his or her real identity. Fugue-like states are associated with retrograde amnesia.
Accelerated long-term forgetting. It occurs when newly learned information decays faster than normal over extended periods. It occurs most frequently in temporal lobe epilepsy, where it is referred to as “transient epileptic amnesia,” but it can also be drug-induced.