This establishes the relationship between the abused chemical agent and the observed clinical effects. Caffeine has been proven to act as an antagonist on adenosine receptors, which acts as a stimulant and therefore fulfills this criteria. Symptoms must also not have a more likely clinical cause, such as another type of anxiety disorder, come before the ingestion of the intoxicating substance, or last for an extended amount of time after stopping the use of the substance. Diagnosis also requires that the panic attacks or anxiety due to the use of the intoxicating substance cause a certain amount of disturbance in the patient or lead to deficiency of varying types of daily performance. Diagnostic features
In addition to the criteria above, it is important to recognize that the diagnostic criteria for substance/medication-induced anxiety disorder are not met if the symptoms of panic come before the intoxication by the substance. In caffeine-induced anxiety disorder, a diagnosis will not be made if symptoms of anxiety or panic precede the ingestion of caffeine. Also, if symptoms persist for more than one month after substance intoxication, the diagnosis cannot be made. Persistence and continuation of symptoms beyond the initial consumption of caffeine suggest an alternate diagnosis that would better explain the long-lasting symptoms. Anxiety symptoms caused by caffeine are often mistaken for serious mental disorders including bipolar disorder and schizophrenia, leaving patients medicated for the wrong issue. A caffeine-induced anxiety disorder diagnosis should be made, rather than a substance abuse or intoxication diagnosis, when symptoms of panic attacks or anxiety predominate.
Mobilization of intracellular calcium
At very high concentrations of about 1–2 mM, caffeine lowers the excitability threshold in muscle cells, leading to prolonged contraction. The introduction of such high doses of caffeine allows calcium to enter the muscle cell through the plasma membrane and sarcoplasmic reticulum more readily. Influx of calcium through the membranes in muscle cells requires at least 250 μM of caffeine. Normally, other toxic effects of caffeine begin to occur in concentrations over 200 μM, however average consumption averages lead to concentrations less than 100 μM. This means that calcium influx and mobilization are most likely not the cause of caffeines effect on the central nervous system, and are therefore not the cause of caffeine-induced anxiety disorder. Inhibition of phosphodiesterases
Methylxanthines such as caffeine inhibit the action of cyclic nucleotide phosphodiesterase, which normally acts to break down cAMP. Cyclic adenosine monophosphate, or cAMP, is a second messenger important in many cellular processes and is a critical factor in signal transduction. The inhibition of the phosphodiesterase would lead to a buildup of cAMP, increasing the activity of the second messenger throughout the cell. Though this mechanism is possible, it only occurs after levels of caffeine have reached a toxic level, and therefore it is unlikely to explain the mechanism of caffeine in the brain. Antagonism of adenosine receptors
There are four well-known adenosine receptors found in the body, A1, A2A, A2B, and A3.