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National Institutes of Health (US); Biological Sciences Curriculum Study. NIH Curriculum Supplement Series [Internet]. Bethesda (MD): National Institutes of Health (US); 2007.

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NIH Curriculum Supplement Series [Internet].

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The Essence of Drug Addiction

(NAPS)-The word "addiction" calls up many different images and strong emotions. But what are we reacting to? Too often we focus on the wrong aspects of addiction so our efforts to deal with this difficult issue can be badly misguided.

Any discussion about psychoactive drugs, particularly drugs like nicotine and marijuana, inevitably moves to the question "but is it really addicting?" The conversation then shifts to the so-called types of addiction—whether the drug is "physically" or "psychologically" addicting. This issue revolves around whether or not dramatic physical withdrawal symptoms occur when an individual stops taking the drug, what we in the field call "physical" dependence.

The assumption that follows then is that the more dramatic the physical withdrawal symptoms, the more serious or dangerous the drug must be. Indeed, people always seem relieved to hear that a substance "just" produces psychological addiction, or has only minimal physical withdrawal symptoms. Then they discount its dangers. They are wrong. Marijuana is a case in point here, and I will come back to it shortly.

Defining Addiction

Three decades of scientific research, coupled with even longer clinical experience, has taught us that focusing on this physical vs. psychological distinction is off the mark, and a distraction from the real issue. From both clinical and policy perspectives, it does not matter much what physical withdrawal symptoms occur. Other aspects of addiction are far more important.

Physical dependence is not that important because, first, even the florid withdrawal symptoms of heroin and alcohol addiction can be managed with appropriate medications. Therefore, physical withdrawal symptoms should not be at the core of our concerns about these substances.

Second, and more important, many of the most addicting and dangerous drugs do not even produce very severe physical symptoms upon withdrawal. Crack cocaine and methamphetamine are clear examples. Both are highly addicting, but stopping their use produces very few physical withdrawal symptoms, certainly nothing like the physical symptoms of alcohol or heroin withdrawal.

What does matter tremendously is whether or not a drug causes what we now know to be the essence of addiction: uncontrollable, compulsive drug seeking and use, even in the face of negative health and social consequences. This is the crux of how many professional organizations all define addiction, and how we all should use the term. It is really only this expression of addiction—uncontrollable, compulsive craving, seeking and use of drugs—that matters to the addict and to his or her family, and that should matter to society as a whole. These are the elements responsible for the massive health and social problems caused by drug addiction.

Essence of Addiction

Drug craving and the other compulsive behaviors are the essence of addiction. They are extremely difficult to control, much more difficult than any physical dependence. They are the principal target symptoms for most drug treatment programs. For an addict, there is no motivation more powerful than drug craving. As the movie "Trainspotting" showed us so well, the addict's entire life becomes centered on getting and using the drug. Virtually nothing seems to outweigh drug craving as a motivator. People have committed all kinds of crimes and even abandoned their children just to get drugs.

Rethinking Addiction

Focusing on addiction as compulsive, uncontrollable drug use should help clarify everyone's perception of the nature of addiction and of potentially addicting drugs. For the addict and the clinician, this more accurate definition forces the focus of treatment away from simply managing physical withdrawal symptoms and toward dealing with the more meaningful, and powerful, concept of uncontrollable drug seeking and use. The task of treatment is to regain control over drug craving, seeking and use.

Rethinking addiction also affects which drugs we worry about and the nature of our concerns. The message from modern science is that in deciding which drugs are addicting and require what kind of societal attention, we should focus primarily on whether taking them causes uncontrollable drug seeking and use. One important example is the use of opiates, like morphine, to treat cancer pain. In most circumstances, opiates are addicting. However, when administered for pain, although morphine treatment can produce physical dependence —which now can be easily managed after stopping use—it typically does not cause compulsive, uncontrollable morphine seeking and use, addiction as defined here. This is why so many cancer physicians find it acceptable to prescribe opiates for cancer pain.

An opposite example is marijuana, and whether it is addicting. There are some signs of physical dependence or withdrawal in heavy users, and withdrawal has been demonstrated in studies on animals. But what matters much more is that every year more than 100,000 people, most of them adolescents, seek treatment for their inability to control their marijuana use. They suffer from com pulsive, uncontrollable marijuana craving, seeking and use. That makes it addicting, certainly for a large number of people.

Treating Addiction: Follow the Science

It is important to emphasize that addiction, as defined here, can be treated, both behaviorally and, in some cases, with medications, but it is not simple. We have a range of effective addiction treatments in our clinical toolbox although admittedly not enough. This is why we continue to invest in research, to improve existing treatments and to develop new approaches to help people deal with their compulsive drug use.

Our national attitudes and the ways we deal with addiction and addicting drugs should follow the science and reflect the new, modern understanding of what matters in addiction. We certainly will do a better job of serving everyone affected by addiction—addicts, their families and their communities—if we focus on what really matters to them. As a society, the success of our efforts to deal with the drug problem depends on an accurate understanding of the problem.

Further information on drug abuse and addiction can be found on the NIDA homepage at www.nida.nih.gov. Free publications can be ordered from the National Clearinghouse for Alcohol and Drug Information by calling 1–800–729–6686.


Loucks-Horsley S, Love N, Hewson PW, Stiles KE. Designing professional development for teachers of science and mathematics. Thousand Oaks, CA: Corwin Press; 1998.


Definitions for the following terms were adapted from a variety of sources. Specific sources are listed in the reference section.


The process by which elements move from outside of the body into the blood and other tissues. Food is absorbed through the stomach and intestines. When tobacco is smoked, nicotine is absorbed through the lungs.


A neurotransmitter that may function in the brain to regulate memory and that controls the actions of skeletal and smooth muscle in the peripheral nervous system.

action potential

The electrical part of a neuron's two-part, electrical-chemical message. An action potential consists of a brief pulse of electrical current that travels along the axon. When the action potential reaches the axon terminal, it triggers neurotransmitter release.


Refers to a disease or condition that has a relatively rapid onset, marked intensity and a short duration.


A chronic brain disorder characterized by the loss of control of drug-taking behavior, despite adverse health, social, or legal consequences to continued drug use. Addiction is characterized by relapses during recovery.


A neurotransmitter that binds to the adenosine receptor. Adenosine is a by-product of ATP metabolism and is an important regulator of sleep. Caffeine is an adenosine antagonist.


A chemical that produces a response, such as excitation or inhibition of action potentials when it binds to a specific receptor. Opiates, cannabis, nicotine, and some hallucinogens are agonists.


A psychoactively complex drug in beverages such as beer, wine, and whiskey. Alcohol is a depressant drug with potential for abuse and addiction.

all-or-none phenomenon

The principle that a nerve fiber will respond maximally or not at all to a stimulus. The strength of the impulse is not dependent on stimulus strength.


Stimulant drugs whose effects are very similar to cocaine.


A part of the brain that is an important component of the limbic system.


The neurotransmitter produced in the body that binds to the cannabinoid receptor; this receptor also binds THC, the psychoactive component in marijuana.


A chemical that, when it binds to a receptor, blocks the receptor and prevents it from responding. Antagonists prevent agonists from binding, or attaching, to the receptor. Antagonists include caffeine and naloxone.


The fiber-like extension of a neuron by which the cell carries information to target cells.

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.


A type of glial cell that provides nutrients, support, and insulation for neurons of the central nervous system.


Depressant drugs that produce relaxation and sleep. Sleeping pills such as pentobarbital and secobarbital are barbiturates.


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

blood-brain barrier

A network of tightly packed cells in the walls of capillaries in the brain that prevents many molecules, including poisons, from entering the brain.


The major route by which the fore-brain sends information to, and receives information from, the spinal cord and peripheral nerves.


A long-lasting opiate analgesic that has both opiate agonist and antagonist properties. Buprenorphine may be useful for treating heroin addiction.


A mild stimulant found in coffee and kola nuts. Caffeine is the most widely used drug in the world.

cannabinoid receptor

The receptor in the brain that recognizes anandamide and THC, the active ingredient in marijuana.


The botanical name for the plant from which marijuana comes.


A tube that is inserted into a cavity or duct.

cell body (or soma)

The central structure of a neuron, which contains the cell nucleus. The cell body contains the molecular machinery that regulates the activity of the neuron.

central nervous system

The brain and spinal cord.


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

cerebral cortex

The outer layer of the cerebral hemispheres that controls conscious experience, including perception, emotion, thought, and planning.

cerebral hemispheres

The two specialized halves of the brain. 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.


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


Refers to a disease or condition that persists over a long period of time.


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


Hunger for drugs. It is caused by drug-induced changes that arise from a need of the brain to maintain a state of homeostasis that includes the presence of the drug.


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


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


The neurotransmitter that produces feelings of pleasure when released by the brain reward system.

dopamine transporter

A protein structure on the cell membranes of axon terminals of dopamine-releasing neurons that carries dopamine back into the presynaptic neuron thereby rapidly removing dopamine from the synapse.


A chemical compound or substance that can alter the structure and function of the body. Psychoactive drugs affect the function of the brain, and some of these may be illegal to use and possess.

drug abuse

The use of illegal drugs or the inappropriate use of legal drugs. The repeated use of drugs to produce pleasure, to alleviate stress, or to alter or avoid reality (or all three).

drug addiction

The continued compulsive use of drugs in spite of adverse health or social consequences.

ecstasy (MDMA)

A chemically modified amphetamine that has hallucinogenic as well as stimulant properties.

electroencephalogram (EEG)

A graphic record of the electrical activity of the brain made by attaching electrodes to the scalp.


Something produced by the brain or body.


Peptides with opiate-like effects that bind to opiate receptors. Endorphins are made by neurons and used as neurotransmitters.


One of the endogenous opioids that binds to opiate receptors and is used as a neurotransmitter.


A large molecule that living organisms use to catalyze chemical reactions. Enzymes are used to build, modify, or break down different molecules without themselves being permanently altered or destroyed.

excitatory neurotransmitter

A neurotransmitter that acts to elicit an action potential or make it more likely that one will be elicited.


A process by which secretory products are released from a cell via transport within vesicles to the cell surface and subsequent fusion with the plasma membrane, resulting in the extrusion of the vesicle contents from the cell.


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

frontal lobe

One of the four divisions of each cerebral hemisphere. The frontal lobe is important for controlling movement and associating the functions of other cortical areas.

GABA (gamma-amino-butyric acid)

The major inhibitory neurotransmitter in the brain.

glial cells (glia)

Brain cells that support neurons by performing a variety of "housekeeping" functions in the brain.


The most common excitatory neurotransmitter in the brain.


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


The potent, widely abused opiate that produces addiction. It consists of two morphine molecules linked together chemically.


A brain structure that is involved in emotions, motivation, learning, and memory.


The process of keeping the internal environment of the body stable by making adjustments to changes in the external environment.


The part of the brain that controls many bodily functions, including feeding, drinking, and the release of many hormones.


The act of taking in food or other material into the body through the mouth.


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


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

inhibitory neurotransmitter

A neurotransmitter that acts to prevent a neuron from firing an action potential.


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.

limbic system

A set of brain structures that generates our feelings, emotions, and motivations. It is also important in learning and memory.

localization of function

A principle of brain organization that states that specific places (circuits) in the brain carry out specific functions.

LSD (lysergic acid diethylamide)

An hallucinogenic drug that acts on the serotonin receptor.

magnetic resonance imaging (MRI)

An imaging technique that uses magnetic fields to take pictures of the structure of the brain.


A drug, usually smoked but can be eaten, that is made from the leaves of the cannabis plant. The main psychoactive ingredient is THC.


A drug that is used to treat an illness or disease according to established medical guidelines.


The processes by which the body breaks things down or alters them so they can be eliminated.


A synthetic opiate used to treat cancer pain and heroin addiction.


A commonly abused, potent stimulant drug that is part of a larger family of amphetamines.


The most potent natural opiate compound produced by the opium poppy. Morphine is a very effective medicine for treating pain.


Fatty material that surrounds and insulates axons of some neurons.


A short-acting opiate antagonist that binds to opiate receptors and blocks them, preventing opiates from binding to these receptors.


An opiate antagonist used to treat heroin addiction, and more recently for the treatment of alcohol addiction.

neuron (nerve cell)

A unique type of cell found in the brain and body that is specialized to process and transmit information.


A chemical produced by neurons to carry messages to other neurons.


The process that occurs when a neuron releases neurotransmitters to communicate with another neuron across the synapse.


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


A neurotransmitter and a hormone. It is released by the sympathetic nervous system onto the heart, blood vessels, and other organs, and by the adrenal gland into the bloodstream as part of the fight-or-flight response. Norepinephrine in the brain is used as a neurotransmitter in normal brain processes.


A cluster or group of nerve cells that is dedicated to performing its own special function(s). Nuclei are found in all parts of the brain but are called cortical fields in the cerebral cortex.

nucleus accumbens

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

occipital lobe

The lobe of the cerebral cortex at the back of the head that includes the visual cortex.

opiate receptors

Receptors that recognize both opiates and endogenous opioids. When activated, they slow down or inhibit the activity of neurons on which they reside.


Any of the psychoactive drugs that originate from the opium poppy or that have a chemical structure like the drugs derived from opium. Some opiates (such as opium, codeine, and morphine) are derived from the plant, while others were first synthesized by chemists.


Any chemical that has opiate-like effects; commonly used to refer to endogenous neurochemicals that activate opiate receptors.

parallel processing

The division of an information-processing job into smaller parts that are each handled simultaneously by various cortical fields and brain nuclei.

parietal lobe

One of the four subdivisions of the cerebral cortex; it is involved in sensory processes, attention, and language.

phencyclidine (PCP)

Originally developed as an anesthetic, PCP may act as an hallucinogen, stimulant, or sedative.

pituitary gland

An endocrine organ closely linked with the hypothalamus. The pituitary secretes a number of hormones that regulate the activity of other endocrine organs in the human body.


The capacity of the brain to change its structure and function within certain limits. Plasticity underlies brain functions such as learning and allows the brain to generate normal, healthy responses to long-lasting environmental changes.


A positively charged particle having the same mass and spin as, but opposite charge of, an electron.

positron emission tomography (PET)

An imaging technique for measuring brain function in living subjects by detecting the location and concentration of small amounts of radioactive chemicals.

postsynaptic neuron

A neuron that receives messages from other neurons.

presynaptic neuron

A neuron that releases neurotransmitters into synapses to send messages to other neurons.

psychedelic drug

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

psychoactive drug

A drug that changes the way the brain works.

psychosocial therapy

Therapy that uses a combination of individual psychotherapy and group (social) therapy approaches to rehabilitate or provide the interpersonal and intrapersonal skills an addict needs to live without drugs.


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.


In drug abuse, relapse is the resumption of drug use after trying to stop taking drugs. Relapse is a common occurrence in many chronic disorders, including addiction, that require behavioral adjustments to treat effectively.

resting membrane potential

The difference in electrical charge between the inside and the outside of a nerve cell when the cell is not firing. The inside of a resting neuron has a greater negative charge than the outside of the neuron.


The process by which neurotransmitters are removed from the synapse 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.


The process that reinforces behavior. 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. The activation of this circuit causes feelings of pleasure.

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 absorbing a drug through mucous membranes.


Intense feelings of euphoria a drug produces when it is first consumed.

second messenger

A molecule produced inside neurons as a step in the process of communication between cells. The second messenger lets other parts of the cell know that a specific receptor has been activated, thereby completing the message carried by the neurotransmitter that bound to the receptor. Some receptors (dopamine and opiate receptors, for example) use second messengers. Others (nicotine and GABA receptors, for example) do not.


An increased response to a drug caused by repeated administration. Sensitization is most commonly seen in some responses to stimulants.


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

single photon emission computed tomography (SPECT)

An imaging process that measures the emission of single photons of a given energy from radioactive tracers in the human body.


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, methamphetamine, and methylphenidate (Ritalin).


The site where presynaptic and postsynaptic neurons communicate with each other.

synaptic space (or synaptic cleft)

The intercellular space between the presynaptic and postsynaptic neurons.

temporal lobe

The lobe of the cerebral cortex at the side of the head that hears and interprets music and language.


Located deep within the brain, the thalamus is the key relay station for sensory information flowing into the brain, filtering out important messages from the mass of signals entering the brain.

tetrahydrocannabinol (THC)

The active ingredient in marijuana that is primarily responsible for producing the drug's psychoactive effects.

temporal lobe

One of the four major subdivisions of each hemisphere of the cerebral cortex. It functions in auditory perception, speech, and visual perceptions.


A physiological change resulting from repeated drug use that requires the user to take larger amounts of the drug to get the same effect initially felt from a smaller dose.


A large protein on the cell membrane of the axon terminals. It removes neurotransmitter molecules from the synapse by carrying them back into the axon terminal that released them.

ventral tegmental area (VTA)

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


A membranous sac within an axon terminal that stores and releases neurotransmitter.


Physical symptoms in the body and brain that occur when a person who is physically dependent stops using the drug.

Copyright © 2007-, BSCS.
Bookshelf ID: NBK20368


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