[4] It is found in chocolate, as well as in a number of other foods, including tea (Camellia sinensis), some American hollies (yaupon and guayusa) and the kola nut.

[5][7] Related compounds include theophylline, caffeine, paraxanthine, and 7-methylxanthine, each of which differ in the number or placement of the methyl groups.

[10][11][12] Theobromine is derived from Theobroma, the name of the genus of the cacao tree, with the suffix -ine given to alkaloids and other basic nitrogen-containing compounds.

[29] The primary mechanism of action for theobromine inside the body is inhibition of adenosine receptors.

Compared with caffeine, theobromine is weaker in both its inhibition of cyclic nucleotide phosphodiesterases and its antagonism of adenosine receptors.

[4][32] The potential phosphodiesterase inhibitory effect of theobromine is seen only at amounts much higher than what people normally would consume in a typical diet including chocolate.

[33] At doses of 0.8–1.5 g/day (50–100 g cocoa), sweating, trembling and severe headaches were noted, with limited mood effects found at 250 mg/day.

[34] Also, chocolate may be a factor for heartburn in some people because theobromine may affect the esophageal sphincter muscle in a way that permits stomach acids to enter the esophagus.

[citation needed] The median lethal dose of theobromine for dogs is 100–200 mg/kg (0.0016–0.0032 oz/lb); therefore, a 10 kg (22 lb) dog would need to consume a minimum of 200 g (7.1 oz) of the most theobromine-rich (5 g/kg (0.080 oz/lb)) dark chocolate, or a maximum of 1 kg (2.2 lb) (of theobromine-rich milk chocolate), to have a 50% chance of receiving a lethal dose.

[39] Complications include digestive issues, dehydration, excitability, and a slow heart rate.