- Caffeine consumption: For healthy subjects: Routine consumption of more than 2 units of caffeine per day or subjects who experience caffeine withdrawal headaches or have a history of caffeine withdrawal headaches. (One caffeine unit is contained in the following items: one 6 oz/180 mL cup of coffee, two 12 oz/355 mL (ie, 24 oz/710 mL cola) cans of cola, one 12 oz/355 mL cup of tea, three 1 oz/28 g chocolate bars (ie, 3 oz/85 g chocolate). Decaffeinated coffee, tea, or cola are not considered to contain caffeine.)