His experiments with magnesium showed negative results: https://gwern.net/nootropic/magnesium#experiment-1
He tried LSD microdosing when the internet was convinced it was a miracle, but found no benefit and some concerning negative effects: https://gwern.net/nootropic/nootropics#lsd-microdosing
Contrast those results with some of the unbelievably positive anecdotes you read about magnesium, fish oil, B-vitamins, or even LSD micro dosing causing life changing positive effects.
It’s well known that placebo effect is a strong driver of perceived effects of most supplements. The placebo effect becomes much stronger when people are primed to expect large effects. Not coincidentally, the people who report the most dramatic effects are often those who consume large amounts of podcasts, YouTube videos, or social media influencer content about those supplements. If someone listens to a 3-hour Huberman Lab episode where he explains how a “protocol” or supplement will do amazing things while using (and frequently misusing) lots of neurotransmitter names and underpowered mouse studies, that person might become so primed to expect those effects that they’re nearly guaranteed to happen. In a weird way, that means it does actually work for them, but it’s not necessarily because the supplant is producing the outcome. It’s because they’re so deeply primed to expect the outcome (e.g. feeling more energy, relaxing to fall asleep) that they placebo themselves into making it happen.