How do certain beverages give a feeling of freshness?

Most of the beverages contain alkaloids which act as mild stimulants. Caffeine, for example, is found in coffee, tea, cocoa, milk chocolate and also in cola drinks. Tea has a trace of theophylline. Cocaine is found in cocoa products. These alkaloids are collectively referred to as methyl xanthines. They share a number pharmacological actions of much therapeutic interest: they relax, smoothen the muscles (notable bronchial muscle), and stimulate the central nervous system and cardiac muscle. They induce the kidneys to excrete more urine, stimulate mental activity, quicken the reflexes, increase vigilance and decrease motor reactions time in response to both visual and auditory stimuli. They increase stamina and reduce fatigue. They give the users a feeling of confidence and power. They even induce euphoria in some users. These stimulant effects are short lived: they last for about an hour. They are then subsequently followed by depression. Overdose or repeated use may lead to paranoia, psychosis or hallucinations.