I inquired of Perplexity: Is Prevagen a scam, claiming at first improved cognitive functions, then downgraded to improving memory.

Based on the available evidence, it appears that Prevagen's claims of improving cognitive function and memory are indeed misleading and potentially fraudulent. The Federal Trade Commission (FTC) and New York State Attorney General have taken legal action against Quincy Bioscience, the maker of Prevagen, for making false and unsubstantiated claims about the product's effectiveness.

Key points supporting this conclusion:

The FTC and NY Attorney General filed a lawsuit in 2017 charging Prevagen's marketers with making false and unsubstantiated claims about memory improvement and cognitive benefits1.

The lawsuit states that Prevagen's own clinical study, the Madison Memory Study, failed to show statistically significant improvement in cognitive function compared to a placebo1.

There is no scientific evidence that the active ingredient in Prevagen, a protein derived from jellyfish, can cross the human blood-brain barrier2.The marketing campaign for Prevagen has been described as "a clear-cut fraud" by the New York Attorney General1.

AARP has joined other advocacy organizations in supporting the lawsuit, stating that Prevagen's claims are "unsubstantiated and misleading"3.
The company has made tens of millions of dollars selling Prevagen, which costs between $24 and $68 per bottle, by targeting vulnerable older adults concerned about memory loss13.
While Quincy Bioscience maintains that their product is effective and backed by evidence, the overwhelming consensus from regulatory bodies and consumer protection organizations is that Prevagen's claims are not supported by credible scientific research. The ongoing legal actions and investigations further underscore the questionable nature of Prevagen's marketing claims.