Causes

Drug use or abuse crosses the line into drug addiction when you feel you have to have the drug, and you increase the amount of the drug you take. Various factors, such as your personality, your genetic makeup and peer pressure, affect your likelihood of becoming addicted to a drug. In addition, some drugs such as heroin and cocaine more quickly produce a physical addiction than other drugs do for many people.

Physical addiction appears to occur when repeated use of a drug alters reward pathways in your brain. The addicting drug causes physical changes to some nerve cells (neurons) in your brain.

Neurons use chemicals called neurotransmitters to communicate. Neurons release neurotransmitters into the gaps (synapses) between nerve cells and are received by receptors on other neurons and on their own cell bodies. The changes that occur in this communication process vary with the type of drug to which you're addicted, though researchers have discovered that addictive drugs, such as cocaine and morphine, all affect some nerve endings in the brain in the same manner. If further research confirms this finding, it may be possible to develop a universal drug that could be used to treat all addictions.

Here are some of the ways specific drugs may contribute to addiction:

• Cannabis compounds. The main active agent in cannabis compounds, delta-9-tetrahydrocannabinol (THC), affects the neurotransmitter communication process. Some people perceive the effects of THC as enjoyable, and this sensation reinforces use of the drug. Other people experience anxiety or uncomfortable feelings, which do not reinforce use of the drug.

• Central nervous system depressants. Benzodiazepines and barbiturates produce long-term cellular changes partly by enhancing the actions of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Released into the synapses, GABA binds to receptors and ultimately lowers cell excitability, which slows down brain activity.

• Central nervous system stimulants. These drugs raise the levels of dopamine, norepinephrine and serotonin in the synapses. Brain cells release dopamine as part of the reward system through which you learn to seek stimuli, such as food and sex. Norepinephrine is a hormone released in response to stress. Serotonin is a chemical in the brain that regulates mood. Stimulants block the reabsorption of dopamine after its release and can physically alter the sensitivities of some dopamine and serotonin receptors.

• Opioids. These drugs affect the nerve cells of the reward pathways in your brain in ways similar to that of stimulants, producing positive reinforcement for the use of these drugs. There are opioid receptors in the brain, spinal cord and gastrointestinal tract.

These factors increase the likelihood of your having an addiction to a legal or an illegal drug:

• Personality. If you're a thrill seeker, impulsive and resistant to social norms, you run a greater risk of drug abuse and dependence. As many as half the people addicted to drugs have another psychological problem such as depression, attention deficit disorder and post-traumatic stress disorder. Children who exhibit aggression, a lack of self-control and a difficult temperament may be at greater risk of drug addiction.

• Social environment. Particularly for young people, peer pressure is a strong factor in starting to use and abuse drugs. A lack of attachment with your parents may increase the risk of addiction.

• Anxiety, depression and loneliness. Using drugs can become a way of coping with these painful psychological feelings.

• Genetics. Drug addiction is more common in some families and likely involves the effects of many genes. If you have family members with alcohol or drug problems, you're at greater risk of developing a drug addiction.

• Type of drug. Some drugs, such as heroin and cocaine, more quickly result in physical addiction than do others.

Addiction is a chronic relapsing disorder, meaning you tend to fall back into old addictive behaviors, including drug use, even after treatment. The sooner you seek help, the greater your chances for a long-term recovery. If you're initially reluctant to approach a doctor, help lines or hot lines may be a good place to start to learn about treatment. You can find help lines listed in the phone book or on the Internet.

Because denial is nearly always a characteristic of addiction, people who are addicted to or who abuse drugs often won't seek medical treatment on their own. Family members, friends or co-workers may need to persuade someone to undergo screening for drug addiction. Breaking a drug addiction may involve counseling, an outpatient treatment program or residential treatment.

Diagnosing a drug addiction often starts at the family doctor level, perhaps after one family member has raised concerns about another family member's behavior. Your doctor may ask questions about your frequency of drug use, whether any family member has criticized your drug use or whether you've ever felt you might have a problem.

A definitive diagnosis of drug addiction usually occurs after an evaluation by a psychiatrist, psychologist or a specialized addiction counselor. Blood tests often aren't able to result in a diagnosis of a drug addiction, but these tests can help a doctor detect the presence of a drug when its use has been denied.

Aside from the physical and psychological problems they cause, dependence on drugs can create a number of other disruptions in your life:

• Family. Behavioral changes may cause marital or family strife.

• Work. Work performance may decline, and you may be absent from work more often.

• Social. You may lose or alienate longtime friends.

• School. Academic performance and motivation to do well in school may suffer.

• Legal. Stealing to support your drug addiction and driving while impaired are just two of the potential legal problems drug addiction can cause.

• Financial. Spending money to support your habit takes away money from your other needs, could put you into debt, and could lead you into behaviors that are contrary to your values.

• Health. Drug use and addiction has many physical consequences that vary depending on which drug you use. Using drugs may make you more likely to participate in other unsafe behaviors, such as sharing needles or having unprotected sex, which can increase your chances of contracting HIV or hepatitis. People who are addicted to drugs are also at a higher risk of overdosing because addicts need more and more of the drug to achieve the same feeling.