You have to distinguish hormonal regulatory mechanisms that are externally vs internally triggered if you're going to discuss decreased natural synthesis. Oral

You have to distinguish hormonal regulatory mechanisms that are externally vs internally triggered if you're going to discuss decreased natural synthesis. Oral testosterone? Pituitary measures it and says to the testicles, "we're good here" and testicles atrophy. Oral prednisone? Pituitary says to adrenals "we're good" and adrenals shut down cortisol production. Melatonin, however, is externally regulated through blue light suppression. So taking it doesn't engage any feedback inhibition, it just increases blood concentration.