Melatonin
Hormone signaling light exposure; endogenous production varies with seasons; supplements are often supra-physiological and require caution, especially during pregnancy.
Videos Mentioning Melatonin

YOU DON'T KNOW HOW MELATONIN WORKS!
The Diary Of A CEO
A hormone that regulates sleep rhythm; described as a sleep regulator rather than a sleep initiator and noted to interact with various medications.

Using Light (Sunlight, Blue Light & Red Light) to Optimize Health | Huberman Lab Essentials
Andrew Huberman
Hormone signaling light exposure; endogenous production varies with seasons; supplements are often supra-physiological and require caution, especially during pregnancy.

Controlling Your Dopamine For Motivation, Focus & Satisfaction
Andrew Huberman
Sleep aid mentioned as a supplement people sometimes use; included among substances affecting dopamine-related processes.

Dr. Satchin Panda on Time-Restricted Feeding and Its Effects on Obesity, Muscle Mass & Heart Health
FoundMyFitness

Weak Muscle Growth Beliefs (Episode 140)
Stronger By Science
An anecdotal reference to a widely cited but possibly non-existent study about melatonin's effects and lack of side effects.