the main effective components caffeinated coffee and its structural analogs theophylline has a strong central excitation.But  more caffeine and theophylline keep longer.People taking caffeine or often table drinking caffeinated beverages.
Sleep now disappear, relieve fatigue, and the thought is agile.Increasing doses, central excitatory effect more apparent, tension, anxiety, restlessness, insomnia, tremor, etc.Larger doses are produced by local or systemic spasm.The effect of theophylline in this respect is stronger than the caffeine.Methyl yellow purine compounds such as caffeine, theophylline can increase the sensitivity of the respiratory center for CO2.Excitation were made of the respiratory center, this kind of role in Cheyne - Stoke breathing (Cheyne - Stoke respiration) and premature infant apnea pathological state and with opioids inhibit breathing under the condition of more obvious.These compounds can be cause nausea and vomiting, this part related to its central role.Taking 85-250 mg of caffeine can make mental Labour work for a long time, the reaction time shortened, but involves delicate muscle coordination and accurate timing or arithmetic work ability declined.Have a phobia patients is especially sensitive for methyl xanthine compounds, in one study, most of these patients taking caffeine plasma concentration up to eight mu g/ml in the performance anxiety, fear, and fear of other typical symptoms.When were the pharmacological inhibition of the central nervous system, low doses of caffeine, such as methyl xanthine central stimulant compounds can be obvious.Other data show that these compounds can be specifically against opiates, including analgesia effect.Intrathecal injection in mice does not produce hyperalgesia doses of caffeine can improve the median effective dose of morphine analgesia.But there is no evidence that alcohol, caffeine, can improve the brain function.Studies have shown that long-term use of caffeine can produce tolerance and drug dependence.

2. The role of smooth muscle: 

    methyl xanthine compounds can relax smooth muscle, is one of the most important of airway smooth muscle relaxation, especially in the clinical use of drugs in asthma, and the experiment that under the condition of airway smooth muscle contraction effect is particularly obvious.Theophylline is smooth muscle relaxation of this kind of compounds in the most effective medicine, but the mechanism remains unclear.In addition, this kind of compounds can specificity of opioid drug effects on gastrointestinal tract.