In the DSM-IV-TR, substance-related disorders are divided to depressants (alcohol, barbiturates and benzodiazepines), stimulants (amphetamine, nicotine, cocaine and caffeine), opiates (codeine, heroin and morphine), and hallucinogens (marijuana and LSD). Specific diagnoses are further classified as substance dependence, substance abuse, substance intoxication and substance withdrawal.

Give a brief definition of addiction, in your own words. What are the similarities and differences in the levels of involvement in the given substance-related phases of addiction: use, intoxication, abuse and dependence? Describe why people continue to use substances, despite of the negative consequences.