There are dozens of illegal addictive substances, such as cocaine and methamphetamine, but many others are not only legal, they are easily accessible in almost every home. Caffeine, aerosols, alcohol, nicotine and prescription medicines can all be addictive. A compulsive need for a substance that is habit-forming -- legal or not -- is an addiction.
How Addictive Substances Affect the Brain
Addictive substances change brain chemistry by flooding the brain's so-called "reward circuit" with dopamine, a chemical that regulates pleasure, attention, cognition and other functions. They do this in one of two ways: imitating brain chemicals or causing the brain to release larger amounts of naturally occurring chemicals.
As a key to survival, the brain is set up to make sure people repeat rewarding activities. The overstimulation of pleasurable sensations teaches the brain to repeat the activity, which leads to a craving that's often beyond a person's control. Over time, images of an addict's brain shows physical alterations in the areas of judgment, learning, memory and impulse control.
Kinds of Addictive Substances
Addictive substances can affect the brain in different ways. Stimulants make a person feel more energetic, and depressants bring a feeling of relaxation. Hallucinogens change the way someone experiences reality. Some drugs fall into more than one classification.
Addictive substances can be legal, illegal or prescription-only.
Legal Addictive Substances
Substances which are legal and readily available include:
- Caffeine: Coffee, tea, soda, sports drinks. Coffee has roughly twice as much caffeine as other sources. Moderate consumption is three cups or less of coffee per day. Ten cups is considered excessive and results in nervousness, sleeping difficulty, increased heartbeat, headaches, anxiety and nausea.
- Nicotine: Cigarettes, cigars, nicotine patches. Both coffee and nicotine are stimulants that not only increase dopamine levels, but boost adrenaline. Increased adrenaline raises the user's heart rate and blood pressure, and interferes with the release of insulin by the pancreas, leading to elevated blood sugar. Nicotine can also act as a depressant.
- Alcohol: Wine, beer, liquor. Alcohol is a depressant that affect neurons in the central nervous system which leads to relaxation, drowsiness, lack of inhibition, sleep, coma and even death. Addiction to alcohol is called alcoholism.
- Inhalants: Aerosols, solvents, gases and nitrates. Products range from paint thinners to hair spray to propane tanks, and inhalation results in a high similar to that of alcohol. Even one-time use of inhalants can kill or cause heart failure.
Controlled Addictive Substances
Some substances are available by prescription only.
- Amphetamines: Speed, crystal meth. Stimulants that boost alertness and concentration. Adderall, dexedrene and other drugs are normally prescribed for treatment of attention deficit hyperactive disorder. Abuse occurs when they're taken in quantities other than those prescribed or by someone other than the intended patient.
- Sedative-hypnotic drugs: Benzodiazepines Xanax, Valium, barbiturates, Seconol, phenobarbital. Benzodiazepines are also known as depressants because they depress brain activity. These drugs are prescribed for insomnia, anxiety, seizures and symptoms of bipolar and manic depressive disorder. Even a small overdose of barbiturates used for anesthesia can result in coma, respiratory distress or death.
- Opioids: Heroin, morphine, oxycodone, codeine and other narcotic pain relievers are very useful when prescribed. They interfere with the way pain messages are sent to the brain and how they brain receives them. Heroin, an illegal drug processed from the poppy-plant product, morphine, is highly addictive. Can be injected, smoked or snorted.
Illegal Addictive Substances
Some substances are illegal in all cases, but can still be widely available.
- Cannabis: Marijuana, grass, pot, hashish. The most commonly used illegal drug in the U.S., it relaxes the user and concentrated doses may bring euphoria, hallucinations or paranoia. Long-term use can be addictive for some people. Prescribed legally in some states for medical use because it curbs nausea.
- Cocaine: Coke, crack. Brings users a strong sense of euphoria and energy before leading to agitation, depression and paranoia. A white powder, cocaine comes from the coco plant and is the second most-used illegal drug in America. Can be snorted, sniffed, injected or smoked (crack).
- Hallucinogens: LSD, ecstasy. Changes the way users perceive time, motion, colors, sound and their own thoughts. Disruption of normal thinking can lead to dangerous behavior.
- Phencyclidine (PCP): Angel dust. Anesthetic approved only for animal use. A hallucinogen that has sedative qualities producing a dissociative state, or out-of-body experience, along with a euphoric rush. Can be sprinkled on marijuana or other substances and smoked, snorted or taken in pill form. Users can become violent or suicidal, and experience muscle contractions so severe they can lead to bone fractures.
Related Addictive Substances Resources
About.com Addiction: What is an Addiction? 
About.com Addiction 
About.com Sports Medicine: Amphetamines 
About.com Post Traumatic Stress (PTSD): Benzodiazepines 
About.com Coffee & Tea: Caffeine 
About.com Alcoholism: Cocaine 
About.com Psychology: Depressants 
About.com Dopamine dopamine
About.com Alcoholism: Hallucinogens 
About.com Alcoholism: Inhalants 
About.com Alcoholism: Marijuana 
About.com Quit Smoking: Nicotine 
About.com Pain: Opioids 
About.com Alcoholism: PCP 
About.com Alcoholism: Prescription Drugs 
About.com Bipolar: Sedatives 
About.com Sports Medicine: Stimulants 
About.com Addictions: Symptoms and Substances 
About.com Alcoholism: Substance Abuse 
Cleveland Clinic Heroin 
Cleveland Clinic Pain Medication 
Cleveland Clinic Cocaine and Crack 
Drug Rehab Treatment Addictive Drugs 
Freedom House Recovery Center Opiates 
Patient Information Harvard Sedatives 
Mission Labs Aerosol Products 
National Institute on Drug Abuse Brain Changes 
Quitters Guide Nicotine Depressant 
U.S. Drug Enforcement Administration Hashish