Well established - The Science Behind Stuff

Does niacinamide actually do anything for your skin?

TL;DR Yes, niacinamide has real, replicated clinical evidence behind it — mostly for reducing hyperpigmentation, improving skin barrier function, and modestly reducing sebum production

Supplements — Well established

Does melatonin actually help you sleep, and is a lower dose better?

TL;DR Melatonin does help with sleep, but the effect is smaller than most people expect and works mainly by shifting your circadian timing

Skin — Well established

Does retinol actually work, and how is it different from prescription retinoids?

TL;DR Retinol works. It's a vitamin A derivative that your skin converts, in two enzymatic steps, into retinoic acid — the same