A

Addiction: A chronic, relapsing disease characterized by compulsive drug-seeking and abuse and by long-lasting changes in the brain.

Amphetamine: A stimulant drug with effects that are similar to cocaine.

Amyl nitrite: A yellowish oily volatile liquid used in certain diagnostic procedures. Illegally diverted ampules of amyl nitrite are called "poppers" or "snappers" on the street. By inhaling its vapors, abusers seek to enhance a sexual experience.

Anabolic/androgenic steroids: Male hormones, principally testosterone, that are partially responsible for the tremendous developmental changes that occur during puberty and adolescence. Male hormones have androgenic and anabolic effects.

Anabolic effects: Accelerated growth of muscle, bone, and red blood cells; decrease in body fat; and enhanced neural conduction.

Analgesics: A group of medications that reduce pain.

Androgenic effects: Changes in primary and secondary sexual characteristics.

Anesthetic: An agent that causes insensitivity to pain and is used for surgeries and other medical procedures.

Axon: The fiber-like extension of a neuron by which the cell carries information from the cell body to the axon terminal.

Axon terminal: The structure at the end of an axon that produces and releases chemicals (neurotransmitters) to transmit the neuron's message across the synapse.

B

Barbiturate: A type of central nervous system (CNS) depressant often prescribed to promote sleep.

Behavioral treatments: A set of treatments that focus on modifying thinking, motivation, coping mechanisms, and/or choices made by individuals.

Benzene: Used as an inhalant– a volatile liquid solvent found in gasoline.

Benzodiazepine: A type of CNS depressant often prescribed to relieve anxiety. Valium and Xanax are among the most widely prescribed medications.

Bind: The attaching of a neurotransmitter or other chemical to a receptor. The neurotransmitter is said to "bind" to the receptor.

Brainstem: The lower portion of the brain through which the forebrain sends information to, and receives information from, the spinal cord and peripheral nerves. Major functions located in the brainstem include those necessary for survival, e.g., breathing, heart rate, blood pressure, and arousal.

Buprenorphine: Medication approved by the Food and Drug Administration in October 2002 for the treatment of opioid addiction.

Butane: An inhalant– a volatile substance found in lighter fluid.

Butyl nitrite: An illegal substance that is often packaged and sold in small bottles, also referred to as "poppers." Like other organic nitrites, it is used primarily as a sexual enhancer.

C

Cannabinoid receptor: The receptor in the brain that recognizes and binds endogenous cannabinoids like anandamide and the related–but exogenous–molecule Delta-9-tetrahydrocannabinol (THC), the active ingredient in marijuana.

Cannabinoids: Chemicals produced naturally that bind to cannabinoid receptors. They are involved in a variety of mental and physical processes, including pain regulation, food intake, and reward.

Cannabis: The botanical name for the plant that produces marijuana.

Carcinogen: A substance that may cause cancer.

Cardiovascular system: The heart and blood vessels.

Cell body (or soma): The central structure of a cell (e.g., neuron) that contains the cell nucleus. The cell body contains both the genetic information and the molecular machinery that translates the information into proteins that determine the function and regulate the activity of the cell.

Central nervous system: The brain and spinal cord.

Cerebellum: A portion of the brain that helps regulate posture, balance, and coordination.

Cerebral cortex: Region of the brain responsible for higher cognitive functions, including language, reasoning, decision-making, and judgment.

Cerebral hemispheres: The two specialized halves of the brain. In right-handed people, the left hemisphere is specialized for speech, writing, language, and calculation; the right hemisphere is specialized for spatial abilities, face recognition in vision, and some aspects of music perception and production.

Cerebrum: The upper part of the brain consisting of the left and right hemispheres.

CNS depressants: A class of drugs that slow CNS function (also called sedatives and tranquilizers), some of which are used to treat anxiety and sleep disorders (includes barbiturates and benzodiazepines).

Coca: The plant, Erythroxylon, from which cocaine is derived. Also refers to the leaves of this plant.

Cocaethylene: A substance produced when coingested cocaine and alcohol are combined in the body (chemically similar to cocaine).

Cocaine: A highly addictive stimulant drug derived from the coca plant that produces profound feelings of pleasure.

Comorbidity: When two disorders or illnesses occur in the same person, they are called comorbid. Drug abuse and other mental illnesses are often comorbid.

Co-occurring disorders: When two disorders or illnesses occur simultaneously in the same person they are co-occurring comorbid disorders.

Crack: Slang term for a smokeable form of cocaine.

Craving: A powerful, often overwhelming desire for drugs.

Cyclohexyl nitrite: An inhalant. Like other nitrites, it acts primarily to dilate blood vessels and to relax muscles and is used mainly as a sexual enhancer. It is usually sold in small bottles, often mislabeled as "video head cleaner," "room odorizer," "leather cleaner," or "liquid aroma."

D

Dendrite: The specialized branches that extend from a neuron's cell body and function to receive messages from other neurons.

Dependence: Physical dependence is a physiological state that can occur with regular illicit or prescription drug use and results in withdrawal symptoms when drug use is abruptly discontinued. Dependence is also the term used for addiction in the Diagnostic and Statistical Manual of Mental Disorders.

Depressants: Drugs that relieve anxiety and produce sleep. Depressants include barbiturates, benzodiazepines, and alcohol.

Detoxification: A process that enables the body to rid itself of a drug. Medically assisted detoxification may be needed to help manage an individual's withdrawal symptoms. Detoxification alone is not treatment, but is often the first step in a drug treatment program.

Dopamine: A brain chemical, classified as a neurotransmitter, found in regions of the brain that regulate movement, emotion, motivation, and pleasure.

Drug: A chemical compound or substance that can alter the structure and function of the body. Psychoactive drugs affect the function of the brain.

Drug abuse: The use of illegal drugs or the inappropriate use of legal drugs. The repeated use of drugs to produce pleasure, alleviate stress, and/or alter or avoid reality.

Drugged driving: Driving a vehicle while impaired due to the lingering, intoxicating effects of recent drug abuse.

E

Ecstasy (MDMA): 3,4-methylenedioxymethamphetamine (MDMA) is a mood- and perception-altering drug that is chemically similar to hallucinogens and stimulants.

Endogenous: Something produced by the brain or other parts of the body.

Ether: A volatile liquid with a characteristic odor. Was used as a medical anesthetic, but ether's highly flammable properties limit its current usage.

F

Fluorinated hydrocarbons: Gases or liquids commonly found in refrigerants, fire extinguishers, solvents, and anesthetics. Freon is one class of fluorinated hydrocarbons.

Forebrain: The largest division of the brain, which includes the cerebral cortex and basal ganglia. It is credited with the highest cognitive functions.

Frontal lobe: One of the four divisions of each cerebral hemisphere. The frontal lobe is important for decision-making, planning, and judgment.

G

Generational forgetting: Term to describe when the knowledge of adverse consequences experienced by a particular generation or population is lost by a subsequent generation.

H

Hallucinations: Perceptions of something (such as an image or a sound) that does not exist in the real world. Hallucinations usually arise from a disorder of the nervous system or as an effect of a hallucinogenic drug, such as LSD.

Hallucinogens: A diverse group of drugs that alter perceptions, thoughts, and feelings. Hallucinogenic drugs include LSD, mescaline, and psilocybin (magic mushrooms).

Halothane: An inhalant– a medical anesthetic gas.

Heroin: A synthetic opioid related to morphine (diacetyl morphine). It is more potent than morphine and is highly addictive.

Hexane: A hydrocarbon volatile liquid found in glue or gasoline.

Hippocampus: An area of the brain crucial for learning and memory.

Hypothalamus: A part of the brain that controls many bodily functions, including feeding, drinking, thermoregulation, and the release of many hormones.

I

Ingestion: The act of taking food or other substances into the body through the mouth.

Inhalant: Any drug administered by breathing in its vapors. Inhalants are commonly organic solvents, such as glue and paint thinner, or anesthetic gases, such as nitrous oxide.

Inhalation: The act of administering a drug or combination of drugs by nasal or oral respiration, as well as the act of drawing air or other substances into the lungs. Nicotine in tobacco smoke enters the body by inhalation.

Injection: A method of administering a substance, such as a drug, into the skin, subcutaneous tissue, muscle, blood vessels, or body cavities, usually by means of a needle. Intravenous drug use: The act of administering drugs directly into blood vessels using a hypodermic needle and syringe.

L

Limbic system: A set of subcortical brain structures that are involved with feelings, emotions, and motivations. It is also important for learning and memory.

LSD (lysergic acid diethylamide):  A hallucinogenic drug that acts on the serotonin receptor.

M

Marijuana: A drug, usually smoked but sometimes ingested, that is made from the leaves of the cannabis plant. The main psychoactive ingredient is Delta-9-tetrahydrocannabinol (THC).

Medication: A drug that is used to treat an illness or disease according to established medical guidelines. If the medication contains one or more controlled substances, it must be prescribed by a licensed physician.

Methadone: A long-acting synthetic opioid medication that is effective in treating opioid addiction and pain.

Methamphetamine: An abusable, potent stimulant drug that is part of the larger class of amphetamines.

Methylphenidate (Ritalin/Concerta): Methylphenidate is a CNS stimulant. It has effects similar to, but more potent than, caffeine and less potent than amphetamines. It has a notably calming and "focusing" effect on patients with attention-deficit hyperactivity disorder, particularly children.

Myelin: Fatty material that surrounds and insulates axons of most neurons to ensure a high level of electrochemical conductance.

N

Neuron (nerve cell): A unique type of cell found in the brain and throughout the body that specializes in the transmission and processing of information.

Neurotransmission: The process that occurs when a neuron releases neurotransmitters into the synapse to communicate with other neurons.

Neurotransmitter: A chemical produced by neurons to carry messages to adjacent neurons.

Nicotine: The addictive drug in tobacco. Nicotine activates a specific type of acetylcholine receptor.

Nitrites: A special class of inhalants that act primarily to dilate blood vessels and to relax the muscles. Whereas other inhalants alter mood through their effects on brain physiology, nitrites are used primarily as sexual enhancers. (See also amyl nitrite and butyl nitrite.)

Nitrous oxide: An inhalant. A medical anesthetic gas, often used in dentistry, that is also called "laughing gas" and is found in whipped cream dispensers.

Noradrenaline: A neurotransmitter that is made in the brain and influences, among other things, the function of the heart.

Nucleus: A cluster or group of nerve cells that is dedicated to performing a distinct function(s). Nuclei are found throughout the brain but are called cortical fields in the cerebral cortex. (See "cell body" above for definition within a cell.)

Nucleus accumbens: A part of the brain reward system, located in the limbic system, that processes information related to motivation and reward. Nearly all drugs of abuse act directly or indirectly on the nucleus accumbens to reinforce drug taking.

O

Occipital lobe: The portion of the cerebral cortex located at the back of the head that includes the visual cortex.

Opiates (or opioids): Controlled substances most often prescribed for the management of pain. They are natural or synthetic chemicals based on opium's active component "morphine" that work by mimicking the actions of pain-relieving chemicals produced in the body, such as enkephalin and endorphin, which are also referred to as endogenous opioids.

P

Parietal lobe: One of the four subdivisions of the cerebral cortex, it is involved with sensory processes, attention, and language.

Polyneuropathy: A neurological disorder that occurs when many peripheral nerves throughout the body undergo permanent change or malfunction simultaneously.

Prescription drug abuse: The intentional misuse of a medication outside of the normally accepted standards of its use.

Prescription drug misuse: Unintentional use of medication in a manner other than that prescribed.

Psychedelic drug: A drug that distorts perception, thought, and feeling. This term is typically used to refer to drugs with hallucinogenic actions like those of LSD.

Psychoactive: Having a specific effect on the brain.

Psychoactive drug: A drug that changes the way the brain works.

Psychotherapeutics: Drugs that have an effect on the function of the brain, some of which are used to treat psychiatric disorders. They include antidepressants, mood stabilizers, CNS depressants, stimulants, and opioids.

R

Receptor: A large molecule that recognizes specific chemicals (normally neurotransmitters, hormones, and similar endogenous substances) and transmits the message carried by the chemical into the cell on which the receptor resides.

Relapse: In drug abuse, relapse is the resumption of drug use after an attempt to stop taking drugs. Relapse is a common occurrence in many chronic disorders, including addiction, that require frequent behavioral and/or pharmacologic adjustments to be treated effectively.

Reuptake: The process by which neurotransmitters are removed from the synaptic space by being "pumped" through transporters back into the axon terminals that first released them.

Reuptake pump (transporter): The large molecule that actually transports neurotransmitter molecules back into the axon terminals that released them.

Reward: The process that reinforces behavior or increases its likelihood of recurrence. It is mediated at least in part by the release of dopamine into the nucleus accumbens. Human subjects report that reward is associated with feelings of pleasure.

Reward system (or brain reward system): A brain circuit that, when activated, reinforces behaviors. The circuit includes the dopamine-containing neurons of the ventral tegmental area, the nucleus accumbens, and part of the prefrontal cortex.

Route of administration: The way a drug is put into the body. Drugs can enter the body by eating, drinking, inhaling, injecting, snorting, smoking, or absorption through mucous membranes.

Rush: A surge of pleasure (euphoria) that rapidly follows the administration of some drugs.

S

Sedatives: Drugs that promote sleep, suppress anxiety, and relax muscles; the National Survey on Drug Use and Health (NSDUH) classification includes benzodiazepines, barbiturates, and other types of CNS depressants.

Serotonin: A neurotransmitter that regulates many functions, including mood, appetite, and sensory perception.

Stimulants: A class of drugs that elevates mood, increases feelings of well-being, and increases energy and alertness. These drugs produce euphoria and are powerfully rewarding. Stimulants include cocaine, amphetamine, methamphetamine, and methylphenidate.

Sudden sniffing death: A type of death that can occur when inhaled fumes fill up the cells in the lungs with poisonous chemicals, leaving no room for the oxygen needed to breathe. This lack of oxygen can lead to suffocation, respiratory failure, and death.

Synapse: The site where presynaptic and postsynaptic cells communicate with each other.

Synaptic space (or synaptic cleft): The intercellular space between the presynaptic and postsynaptic neurons where neurotransmitters are released.

T

Temporal lobe: The lobe of the cerebral cortex at the side of the head that integrates visual and auditory perceptions.

Tetrahydrocannabinol: See "THC."

Thalamus: Located deep within the brain, the thalamus is the key relay station for sensory information flowing to the cortex, selecting important messages out of the background noise produced by the many signals entering the brain.

THC: Delta-9-tetrahydrocannabinol; the main active ingredient in marijuana, which acts on the brain to produce marijuana's psychoactive effects.

Tobacco: A plant widely cultivated for its leaves, which are used primarily for smoking; the tabacum species is the major source of tobacco products.

Tolerance: A condition in which higher doses of a drug are required to produce the same effect achieved during initial use, which often leads to physical dependence.

Toluene: A light colorless liquid solvent found in many commonly abused inhalants, including model airplane glue, paint sprays, and paint and nail polish removers.

Tranquilizers: Drugs prescribed to promote sleep or to reduce anxiety; the NSDUH classification includes benzodiazepines, barbiturates, and other types of CNS depressants.

Transporter: A large protein on the cell membrane of the axon terminals. It removes neurotransmitter molecules from the synapse and transports them back into the axon terminal that released them.

Trichloroethylene: A liquid used as a solvent and, in medicine, as an anesthetic and analgesic. It is found in cleaning fluid and correction fluid.

V

Ventral tegmental area: The group of dopamine-containing neurons that make up a key part of the brain reward system. These neurons extend axons into the nucleus accumbens and beyond to the prefrontal cortex.

Vesicle: A membranous sac within an axon terminal that stores neurotransmitters and releases them when needed.

W

Withdrawal: Symptoms that occur after chronic use of a drug has been abruptly reduced or stopped. Symptom severity depends on the type of drug, the dosage, and how long and how frequently it has been taken.