The internet is abuzz with tributes to a liquid chemical called methylene blue that is being sold as a health supplement. Over the past five or 10 years, methylene blue has come to be touted online as a so-called nootropic agent – a substance that enhances cognitive function. Vendors claim that it amps up brain energy, improves memory, boosts focus and dispels brain fog, among other supposed benefits. Health influencers, such as podcaster Joe Rogan, have sung its praises. In February 2025, shortly before he was confirmed as health and human services secretary, Robert F. Kennedy Jr. appeared in a...