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Drug Classification
This section describes several common schemes for classifying drugs
with psychoactive
properties. For common street names of illicit drugs, see Illicit Drug Index.
For a
brief commentary regarding the commonly used distinction between
“hard” and “soft” drugs, see Hard and Soft
Drugs.
Chemical Structure
Compounds are often classified according to their chemical structures. Although this is useful for medicinal chemists, it does not provide a meaningful classification scheme for categorizing drug effects. Some compounds with similar chemical structures produce very similar biological effects (e.g., morphine, heroin), but others which belong to the same chemical class often produce much different effects (e.g., apomorphine, nalorphine). Furthermore, compounds which differ in chemical structure often produce similar biological effects (e.g., amphetamine, cocaine).
Pharmacological Activity
This scheme classifies drugs according to their primary pharmacological activity. All compounds produced multiple effects, so what is consider the primary effect and what is considered the secondary effect varies as a function of reference point. Often the primary therapeutic use of a compound is considered its primary effect and thus used to classify it pharmacologically.
The classification scheme given below focuses on each compound's
main
psychotropic effects which in some cases classifies it differently from
what
might be considered its primary pharmacological effect (i.e., based on
therapeutic use). For example, pseudoephedrine is a popular
decongestant that
has mild stimulatory properties. Pseudoephedrine's decongestant
effect
might be considered its primary effect, while its stimulatory effect
would be
considered a secondary side-effect. However, from a
psychopharmacological
perspective, pseudoephedrine's stimulatory effect is its primary effect
and its
decongestant action is a secondary (although therapeutically more
useful)
effect. Therefore, pseudoephedrine is classified below as a mild
stimulant like
caffeine and nicotine.
|
Drug Class |
Primary Effects/Approved Medicinal Uses |
Examples |
|
analgesia, cough suppression, antidiarrhea, suppression of opiate withdrawal, sedation; currently used therapeutically for the first four effects |
opium, morphine, codeine, heroin (diacetyl morphine), fentanyl, methadone, meperidine, L-alpha-acetylmethadol (LAAM) |
|
|
block the effects of narcotics; used to treat opiate overdose |
naloxone, naltrexone |
|
|
stimulate psychological and sensory-motor functioning; used therapeutically to treat ADHD and narcolepsy, sometimes as an appetite suppressant, occasionally antifatigue, formerly for asthma and for sinsus decongestion |
amphetamine, methamphetamine, cocaine, methylphenidate |
|
|
similar to psychomotor stimulants but with much less efficacy; various therapeutic effects including caffeine compounded with aspirin in some OTC pain relievers, ephedrine in OTC asthma medicines, pseudoephedrine in OTC sinus decongestants and OTC appetite suppressants |
caffeine, nicotine, ephedrine, pseudoephedrine |
|
|
general decrease in CNS arousal/excitability level; used therapeutically for anesthetic, anticonvulsant, sedative, and hypnotic effects |
thiopental, secobarbital, pentobarbital, phenobarbital |
|
|
general decrease in CNS arousal/excitability level, but low dose are somewhat selective for anxiety and much less sedative than barbiturates; used therapeutically as anxiolytics, benzodiazepines also as anesthetics and anticonvulsants |
includes two subclasses: benzodiazepines (e.g.,. diazepam, chlordiazepoxide, flunitrazepam [Rohypnol]) and muscle relaxants (e.g., meprobamate) |
|
|
general sedation at high doses, with selective antipsychotic activity at lower doses; used therapeutically to treat schizophrenia and other major psychotic disorders |
haloperidol, pimozide, flupenthixol, chlorpromazine, spiroperidol, clozapine |
|
|
no perceptible CNS effects in normals, but effectively alleviate depression in many depressives; used therapeutically to treat depression |
includes three subclasses: monoamine oxidase inhibitors (e.g., pargyline), tricyclic antidepressants (e.g., amitriptyline, desmethylimipramine), and selective serotonin reuptake inhibitors (SSRIs: e.g., sertaline) |
|
|
Antimanic |
dampens extreme mood swings in some people; used to treat manic-depressive (bipolar) disorders |
lithium |
|
Alcohol |
general decrease in CNS arousal/excitability level; no current therapeutic uses, but formerly used as an anesthetic and a sedative |
ethyl alcohol (other alcohols have similar actions but are associated with very toxic effects, e.g., methanol) |
|
general decrease in CNS arousal/excitability level; used therapeutically for anesthesia |
nitrous oxide, halothane, ether |
|
|
Volatile Solvents |
produce feelings of intoxication, can produce hallucinations at high doses; no therapeutics uses (all can cause marked brain damage in moderately low concentrations |
toluene, benzene, naphtha |
|
produce altered states of consciousness; hallucinogenics produce hallucinations sometimes reported as "mystic" experiences; cannabinoids usually produce increased feelings of "well being" and "mellow" intoxication; the "pleasantness" of the states produced by both classes probably depends partially on expectancies; no approved therapeutic uses, but cannabinoids are being increasingly used for their antinausea, anxiolytic, and appetite-stimulating effects in severely ill patients (e.g., AIDS) |
includes two subclasses: hallucinogenics (e.g., lysergic acid diethylaminde [LSD], mescaline, psilocybin) and cannabinoids (e.g., marijuana, hashish). |
|
|
Stimulatory Hallucinogenics (cf. former psychotomimetics) |
produce a mixture of psychomotor stimulant and hallucinogenic effects, depending on dose and other factors; no therapeutic uses, except phencyclidine as a veterinary anesthetic |
MDMA (ecstasy), phencyclidine (PCP), ketamine (?) |
|
Abbreviations: ADHD, attention deficit hyperactivity disorder; AIDS, acquired immune deficiency syndrome; CNS, central nervous system; OTC, over-the-counter (nonprescription) medicines. |
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DEA Drug Schedules
The Controlled Substances Act of 1970 divided substances to be regulated into 5 schedules. These schedules govern the legal distribution and use of most substances with a significant abuse liability. (For details of the Controlled Substances Act and its revisions, see Appendix C, Agents Manual--DEA SENSITIVE.) The Drug Enforcement Administration is the primary federal agency charged with enforcing these regulations and with coordinating national and international efforts to reduce illicit drug supply. Hence, this classification scheme is often refereed to as the DEA Schedules.
- Schedule I substances have a high abuse liability and no approved medical use. These substances are available for investigational purposes only, and the research protocol must be approved by the Food and Drug Administration (FDA) prior to granting a license for handling Schedule I compounds. Drugs are provided by manufactures under federal contract. Pharmacies do not sell these compounds nor can physicians write prescriptions for them. Special record-keeping and storage procedures are required for all Schedule I substances.
- Schedule II-IV substances have decreasing abuse liabilities (II is the highest) and approved medical uses. Physicians are licensed to prescribe these compounds and pharmacies can dispense them, although pharmacies do not stock all of these substances. Schedule II compounds have more stringent record-keeping and storage requirements than do Schedule III and IV substances.
- Schedule V substances have a recognized abuse liability (and approved medical uses) but are generally not regulated (e.g., they are available without prescription). Many of these substances are used in common, over-the-counter medicines. Including compounds on this schedule facilitates state and local regulations deemed appropriate in some jurisdictions (e.g., An individual state may impose restrictions on some substance considered to have an unexpectedly high abuse liability.).
|
Schedule |
Abuse |
Approved |
Availability |
Examples |
|
Schedule I |
High |
No |
investigational |
|
|
Schedule II |
High |
Yes |
written |
|
|
Schedule III |
Moderately High |
Yes |
written or |
|
|
Schedule IV |
Moderate |
Yes |
written or |
|
|
Schedule V |
Low |
Yes |
prescription |
Robitussin A-C (contains less than 100 mg codeine per 100 ml) |
|
Note: Drugs are continually being reclassified. The above listing (except for Schedule V) is from the information contained on the DEA's license application/renewal form (DEA-225) dated April 1988. |
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Addiction Liability
It is virtually impossible to reach consensual agreement regarding the relative addiction liability of most drugs. However, scientific agreement is generally good regarding the drugs that produce the strongest indications of addiction. These drugs belong to two pharmacological classes—psychomotor stimulants and opiates—and can be considered the prototypical addictive drugs. Agreement is also good regarding the relatively low addiction liability of some over-the-counter medicines, such as aspirin, diphenhydramine (an antihistamine), and pseudoephedrine (a decongestant). Some commonly used substances have controversial addiction liabilities (e.g., caffeine, nicotine).
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