When Myron first encountered the Mordinos, they were farming peyote cacti and trying to sell it to tourists as the "Reno Experience". Unfortunately peyote trips are too long, and profit is generated by fast turn around and a high addiction rate. Furthermore the climate was far too ravaged and irradiated to grow most vegetable matter but the hardiest of plants, so Myron began delving in growing mushrooms. Hallucinogens have low overhead and thrive in plentiful brahmin dung. From there Myron began experimenting with derivatives of lysergic acid diethylamide and psilocybin and THC the active substance in marijuana (unknown to still grow). However the Mordinos still desired something a little harder and more addictive that could get them Redding. The solution to the problem came from the Brahmin fertilizer itself. protein extract was obtained and then corrupted. By placing the augmented Brahmin dung in large vats they could gather the potent drug they were searching for. (from fallout wiki)
yup, there you have it. Whenever you huff up some Jet in FO 3, take delight in the fact that you are taking in "enhanced" Brahmin crap vapors