Pregnenolone is synthesized from cholesterol in the mitochondria of steroidogenic cells. Sitting at the top of the steroid pyramid.
Mechanism: Every other steroid (cortisol, DHEA, progesterone, testosterone, estradiol) descends from pregnenolone. It also has direct neurosteroid activity. NMDA modulation, sigma-1 receptor. Implicated in memory and mood.
Lab range: 30–250 ng/dL, declines with age.
Caveats: Oral supplementation is common; effects are usually subtle. Not a drop-in replacement for downstream hormones, just feedstock. Don't expect dramatic results from pregnenolone alone.