Comparative toxicities of dietary caffeine and theobromine in the rat.

Caffeine, incorporated into pulverized Purina Rat Chow at a concentration of 0.5%, was fed to male Sprague-Dawley rats for 7 or 8 wk and the effects were compared with those of 0.8% dietary theobromine, fed to male rats for 7 wk. Both dietary methylated xanthines produced significant decreases in food consumption and body-weight gain when compared to their respective control groups. Food consumption of caffeine-fed rats was 57.2% of controls and for theobromine-fed rats it was 77.9% of the respective controls. Theobromine produced significant decreases in thymus weights, with caffeine producing smaller decreases. The theobromine-fed rats showed severe testicular atrophy with extensive spermatogenic cell degeneration and necrosis, while the testes of rats fed caffeine for 7 or 8 wk showed only scattered vacuolar degeneration of spermatogenic cells. Caffeine appears to be more potent than theobromine as an anorexic agent in rats, but to be equivalent to theobromine in its potential for inducing thymic atrophy and spermatogenic cell destruction with testicular atrophy.