If insufficient quantities are ingested, the discomfort of withdrawal symptoms usually leads the individual to continue intake, creating an ongoing cycle. As a condition, substance abuse is considered chronic without treatment. In severe cases it can result in death.
Cigarette smoking is perhaps the most common form of substance abuse.
It is addictive both psychologically and physically, due to the effects of nicotine, and is proven to be damaging to health. Another specific form of substance abuse is alcohol abuse, which will be examined in a separate entry. For example, addiction to sedative drugs often causes dysarthria, ataxia, and slowed thinking and movement. Amphetamines, however, often lead to nervousness, agitation, tremor, delirium, panic states, and extreme fatigue. The extent of limitation is usually more severe with longer period of addiction and with increased dosages.