I haven't read this but it contains lots of suggestions about drugs that could impair memory, along with suggestions for medications and other items that might help with memory. Free full text: https://www.ipinnovative.com/media/journals/AnnGeriatrEducMedSci-7-1-22-311.pdf
I suspect that a major cause of memory problems in people over 65 is polypharmacy. And I would also suspect that diets are likely to be poor in hospitals, nursing homes, and retirement homes. Older people still living at home and caring for themselves may lack the energy or motivation or the money to shop for healthy food, and might not be able to cook for the same reasons.
It's ironic that, in the UK, DHEA has been classed as an anabolic steroid and is a category C controlled drug and is thus illegal to buy. You can find it on the government's controlled drugs list as Prasterone (Dehydroepiandrosterone DHEA). DHEA is an over-the-counter supplement in the USA. https://en.wikipedia.org/wiki/Prasterone#Regulation
