Cannabinoids (THC, CBD) don't directly reduce testosterone. Instead, the act of smoking marijuana increases the enzyme aromatase, which converts testosterone into estrogen. Higher estrogen then signals the pituitary to reduce testosterone production, creating an indirect negative feedback loop.

The androgen receptor gene, which dictates how the body responds to hormones like testosterone and DHT, is located on the X chromosome. Since men (XY) inherit their X chromosome from their mother, their genetic predisposition for androgen sensitivity is maternally inherited.

Studies on 2D:4D finger ratios, a proxy for prenatal androgen exposure, found no average difference between gay and straight men. This challenges the "under-androgenized" stereotype and suggests orientation differences may stem from the brain's response to testosterone, not the hormone level itself.

Research shows that the same genetic predispositions for physical aggression (e.g., fighting) in boys can manifest as relational aggression (e.g., social exclusion, reputation damage) in girls. This highlights a common biological root for sex-differentiated expressions of aggression, which can be equally damaging.

The term "hormone resistance" was misleading. Researchers discovered that even in a castrate state, prostate cancer tumors produce their own testosterone locally. This maintained androgen receptor signaling, proving the disease was still "androgen addicted" and opening the door for new targeted therapies.

Distinct neuron populations control mating and aggression. Activating mating neurons in a male mouse's medial preoptic area during a fight causes it to immediately stop attacking and instead attempt to mate with the other male, demonstrating a clear neural override mechanism between competing social behaviors.

In mice, prolonged social isolation causes a dramatic increase in the neuropeptide tachykinin. This neurochemical surge is directly responsible for increased aggression, fear, and anxiety. A drug that blocks the tachykinin receptor can completely reverse these isolation-induced effects.

Stimulating specific aggression neurons in the ventromedial hypothalamus (VMH) of male mice elicits offensive aggression that they find rewarding. Mice will learn to perform tasks, like pressing a lever, for the opportunity to attack a subordinate male, indicating the behavior has a positive valence.

Dr. D'Agostino gives his aging, neutered dogs a Selective Androgen Receptor Modulator (SARM) to stimulate muscle protein synthesis and maintain vitality. This approach is analogous to Testosterone Replacement Therapy (TRT) in humans, aiming to counteract the loss of skeletal muscle mass associated with aging and hormonal changes.