Using marijuana can lead to the development of problems, known as marijuana use disorder, which is addiction. Recent data suggests that 30% of marijuana users suffer from some degree of marijuana use disorder. People who start using marijuana before age 18 are four to seven times more likely to develop a marijuana use disorder than adults. Marijuana use disorders often associated with experiencing withdrawal symptoms when not taking the drug. Regular marijuana users often report irritability, mood and sleep difficulties, decreased appetite, cravings, restlessness, and various forms of physical discomfort that peak within the first week after quitting and last up to two weeks. Marijuana addiction occurs when the brain adapts to large amounts of the drug by reducing its production and sensitivity. Marijuana use disorder becomes addiction when the person cannot stop using the drug even though it interferes with many aspects of their life. Estimates of the number of people dependent on marijuana are controversial, in part because epidemiological studies of substance use often use dependence as a proxy for addiction, even though it is possible to be addicted without being addicted. These studies suggest that 9% of people who use marijuana will become dependent on it, which rises to about 17% in those who start using it young (in their early years).).