How can we tell if someone is abusing or addicted to drugs?

Diagnostic and Statistical Manual - III - R
[DSM-III-R is not currently used but has historical utility.] At least three of the following are necessary; some of the symptoms of the disturbance must have persisted for at least one month or have occurred repeatedly over a longer period of time:

• Substance is often taken in larger amounts or over longer period than intended
• Persistent desire or one or more unsuccessful efforts to cut down or control substance use
• A great deal of time is spent in activities necessary to get the substance (e.g., theft), taking the substance (e.g., chain smoking), or recovering from its effects
• Important social, occupational, or recreational activities given up or reduced because of substance abuse
• Continued substance use despite knowledge of having a persistent or recurrent social, psychological, or physical problem that is caused or exacerbated by use of the substance
• Marked tolerance: need for markedly increased amounts of the substance (> 500/ increase) in order to achieve intoxication or desired effect, or markedly diminished effect with continued use of the same amount
• Characteristic withdrawal symptoms
• Substance often taken to relieve or avoid withdrawal symptoms
• Frequent intoxication or withdrawal symptoms when expected to fulfill major role obligations or when use is physically hazardous

Diagnostic and Statistical Manual - IV

A maladaptive pattern of substance use leading to clinically significant impairment or distress as manifested by three (or more) of the following, occurring at any time in the same 12-month period:

• Substance is often taken in larger amounts or over longer period than intended
• Persistent desire or unsuccessful efforts to cut down or control substance use
• A great deal of time is spent in activities necessary to obtain the substance (e.g., visiting multiple doctors or driving long distances), use the substance (e.g., chain smoking), or recover from its effects
• Important social, occupational, or recreational activities given up or reduced because of substance abuse
• Continued substance use despite knowledge of having a persistent or recurrent psychological, or physical problem that is caused or exacerbated by use of the substance
• Tolerance, as defined by either:
  1. need for read amounts of the substance in order to achieve intoxication or desired effect; or
  2. markedly diminished effect with continued use of the same amount
• Withdrawal, as manifested by either:
  1. characteristic withdrawal syndrome for the substance; or
  2. the same (or closely related) substance is taken to relieve or avoid withdrawal symptoms

International Classification of Diseases - 10
[ICD-10 research criteria differ from the clinical diagnostic quidelines listed here.] Three or more of the following must have been experienced or exhibited at some time during the previous year:

• Difficulties in controlling substance-taking behavior in terms of its onset, termination, or levels of use
• A strong desire or sense of compulsion to take the substance
• Progressive neglect of alternative pleasures or interests because of psychoactive substance use, increased amount of time necessary to obtain or take the substance or to recover from its effects
• Persisting with substance use despite clear evidence of overtly harmful consequences, depressive mood states consequent to heavy use, or drug related impairment of cognitive functioning
• Evidence of tolerance, such that increased doses of the psychoactive substance are required in order to achieve effects originally produced by lower doses
• A physiological withdrawal state when substance use has ceased or been reduced, as evidence by: the characteristic withdrawal syndrome for the substance; or use of the same (or a closely related) substance with the intention of relieving or avoiding withdrawal symptoms