Amphetamine administered during retrieval increased memory errors in a controlled study without increasing the number of correctly remembered items. Memory formation and memory retrieval can respond differently to the same drug.
Ballard, Gallo and de Wit studied 31 healthy young adults. Participants viewed emotional and neutral pictures and words in a drug-free state. Two days later, memory was tested one hour after placebo or 10 or 20 mg dextroamphetamine.
The conditions were counterbalanced and double-blind. This timing isolated a different question from experiments administering a stimulant before the original learning experience.
Dextroamphetamine did not significantly change the number of emotional or unemotional items remembered. Both doses nevertheless increased recall intrusions and false recognition. At 20 mg, it also increased positively rated picture descriptions and words generated during free recall.
These findings make the denominator and error type important. Producing more material that was not actually presented is not the same as remembering more correct material. A positive bias in generated content is also different from a global improvement in accuracy.
General stimulant-enhancement claims cannot answer a phase-specific memory question. A drug that strengthens encoding under one protocol may have different effects when taken only during retrieval.
The observed errors arose on standardized tasks. They do not establish that every amphetamine-exposed person develops false memories or that an individual account of an event is inaccurate.
The study supports examining when exposure occurred relative to the event and the later recollection. It also supports separating correct recall, intrusions and recognition errors rather than treating a single memory score as complete evidence.
The sample involved healthy young adults and selected laboratory doses. It did not validate a toxicology threshold for unreliable testimony, establish effects in every clinical population, or provide a method to adjudicate a particular disputed memory. Such conclusions require independent evidence about the event and the individual.
Related reading: Memory for future intentions.