Cocaine mostly causes levels of dopamine to increase in the brain (most of this effect isn't done by creating more, but by stopping it from being destroyed--inhibiting reuptake). Dopamine is basically the chemical that causes the sensation of pleasure. I'm not really sure if just seeing a "hot girl" would cause it to be created in one's body, but I'm fairly certain it is created during sex... that could be what the show meant.

-AbyssDragon