(c) The alkaloid caffeine is present in both tea and coffee. Caffeine is found in coffee, black and green tea, cocoa, cola soft drinks and energy drinks. It may also be found in chocolate bars, energy bars and medications, such as cough syrup,etc. The higher use of caffeine can cause insomnia, nervousness and restlessness, stomach irritation,nausea and vomiting, increased heart rate and other side effects.