Cocaine is a powerful and highly addictive drug. It is usually snorted, dissolved in water to be injected, or smoked in crystal form (crack). Cocaine affects the central nervous system and interferes with the reabsorption of dopamine and the resulting buildup is what is associated with the "euphoria" the user feels. The duration of the high depends on how fast the drug is absorbed by the body. The faster the absorption the more intense and short lived the high is. Increased use can reduce the period of time the user feels high and can increase the risk of addiction. Some users of cocaine report feelings of restlessness, irritability, and anxiety. A tolerance to the "high" may develop - many addicts report that they seek but fail to achieve as much pleasure as they did from their first experience. Some users will increase their doses to intensify and prolong the euphoric effects. While tolerance to the high can occur, users can also become more sensitive to cocaine’s anesthetic and convulsant effects without increasing the dose taken. This increased sensitivity may explain some deaths occurring after apparently low doses of cocaine. How ever cocaine is used, or how often, users can experience acute cardiovascular or cerebrovascular emergencies such as heart attack or stroke. Death related to cocaine use is most often the result of cardiac arrest or seizure follwed by respitory arrest.