Alcohol consumption increases the toxicity of the pharmacological constituents. Can cause drowsiness. If this happens, lower your dosage or discontinue taking kava. Caffeine is probably the most popular and readily available drug in the world. Caffeine occurs naturally in plants and is found in leaves, seeds, and fruits such as coffee, coca beans, tea leaves, and kola nuts.
Caffeine acts as a mild stimulant to the nervous system.
It increases alertness, attention, and mental ability. Caffeine intake also has negative side effects, which are anxiety, gastrointestinal distress, nervousness, irritability, insomnia, and inability to concentrate. The use of caffeine has been controversial in sport performance since the negative side effects can hamper performance. Some studies have shown caffeine intake prior to exercise can enhance performance while other studies have found caffeine to be of no benefit. While the mechanisms responsible for the improved endurance have not been clearly established, several theories exist.