A drug is a substance other than food that is taken to obtain a desired effect on the mind or body.  By this definition, insulin and penicillin are drugs. (1)

What is a psychoactive drug?

The word "psycho" comes from Greek and means "mind."  A psychoactive drug is a drug that has an effect on the brain and central nervous system. It can affect the way a person thinks, feels or acts.  Psychoactive drugs impact on our thinking, senses, emotions, how awake or sleepy we feel, energy levels, organ functions, hormone levels, coordination and motor control.  By this definition alcohol, heroin and marijuana are psychoactive drugs, but insulin and penicillin are not.  Not all psychoactive drugs are illegal.  For example, morphine and demerol interfere with the reception of pain signals and are therefore psychoactive drugs, but when prescribed by a physician, they are not illegal.  Because of their mood altering properties, psychoactive drugs are the most abused of all drugs.  Alcohol is a drug, and from here on the word "drug" refers to alcohol as well as other types of drugs.  (1)

What is the difference between use and abuse?

Many people who drink or use moderately experience no problems in any area of their lives.  Abuse happens when one crosses that line, and he or she drinks or uses at a level that causes problems in one or more areas of his or her life.  This would include health problems, mental health/emotional problems, family problems, relationship problems, financial problems, work or school problems, social problems, and legal problems.  With a few drugs, the potential dangers are extremely high and they can cause serious problems no matter how or when they are taken.  Examples are PCP (Angel Dust), cocaine or heroin.  There is no such thing as moderate use with these drugs; to use them at all is to abuse them.  (1)  Complete our online questionnaire to help you decide if you have problems in your life because of alcohol or drugs and if you have moved from use to abuse.

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What does dependence mean?

Dependence refers to a physical state where when one stops using a drug or alcohol, withdrawal occurs.  If a person experiences withdrawal symptoms after discontinuing use of drugs or alcohol, then he or she is dependent on that drug or alcohol.  After repeated use of a drug the user's body becomes so accustomed to a particular drug that it can only function normally if the drug is present.  Often the terms addiction and dependence are used to mean the same thing.  Physical dependence is one of the factors contributing to the continued use of drugs.  (1),(2)

What is psychological dependence?

Psychological dependence exists when a drug is so central to a person's thoughts, emotions, and activities that it is extremely difficult to stop using it, or even stop thinking about it.  Like physical dependence, psychological dependence is a cause of continued drug use.  (1)

What is tolerance?

Over time with regular use, a user needs more and more of the drug to get the desired effect.  Increased tolerance means an increased risk for overdose for two reasons.  First, every drug has a main effect (the effect the user wants) and side effects (effects that the user does not want).  Tolerance does not develop evenly to all effects of a drug.  For example, barbiturate users develop tolerance to the desired mood altering effect of the drug faster than they do to the side effect of depressing breathing.  When the user increases the dose to get the desired effect, they risk taking enough to cause them to stop breathing, which of course would cause death.  Second, if a user has not used for a while, tolerance will decrease.  Tolerance to any drug decreases with non-use, and does so faster with some drugs than others.  After a period of abstinence, the dose the user had previously used may now be enough to cause a fatal overdose.  Heroin is a good example of a drug for which tolerance can drop very quickly, and many people die every year from heroin overdose.  (1)

What is withdrawal?

Withdrawal is related to physical dependence and tolerance.  After repeated use over a period of time, the body adjusts itself to enable it to function normally with the presence of the drug.  This could mean that it produces less of a chemical used in the brain that the drug imitates (neurotransmitters).  It could mean that it develops more receptors in the brain to handle the drug.  The body might start producing more enzymes to break the substance down, and hormone levels could change.  When use of the drug stops, the body fails to function normally because it has adjusted to compensate for the presence of the drug, and this abnormal functioning is felt as withdrawal.  The higher the degree of tolerance and dependence, the worse the withdrawal symptoms will be.  Withdrawal to different drugs varies in unpleasantness, severity and risk for death.  Withdrawal from heroin is one of the most unpleasant withdrawals, but withdrawal from heavy barbiturate or alcohol use after a very long period of use has a greater risk of death.  Withdrawal symptoms are usually the opposite of the effects and side effects of the drug.  For example, one of the side effects of heroin is constipation, and one of the withdrawal effects from heroin is diarrhea.  (2)  

What does cross addiction or cross dependence mean?

Drugs can be grouped into different classes according to their effect on the central nervous system (your brain and its connections to the various organs and other parts of your body).  If you are using a drug repeatedly over a period of time, you will develop dependence on that drug.  But you will also develop dependence to other drugs that you have not used that are in the same class as the drug you are using.  This means that when you stop using one drug and begin to experience withdrawal, prescribed use of another drug in the same class might stop or decrease the severity of withdrawal.  An example is the use of methadone (a narcotic) to help heroin (a narcotic) users avoid withdrawal.  Cross addiction has also been used to describe addiction to more than one drug, whether or not it is in the same class.  (2)

What does cross tolerance mean?

Continued use of a drug will build tolerance to that drug, but tolerance might also increase to other drugs in the same class.  For example, use of an opiate drug will cause tolerance to other opiate drugs.  Heroin is a narcotic drug, and so are morphine and demerol.  If a user develops tolerance to heroin, he will also show a tolerance for morphine and demerol without using those drugs regularly.  (2)  It is possible for a person to develop tolerance to general anaesthetic by using drugs in the depressant class.  In some rare cases, people have awakened in the middle of surgery and become conscious of pain, but they remained unable to move or speak to let the surgeon know that they were conscious and feeling pain.  If you use drugs regularly and need medical treatment, it is important to let your doctor know what drugs you use and how often.  

What is synergism?

Synergism refers to the interaction of two drugs in such a way that the total effect is greater than the sum of the individual effects.  (3)  If for example you know that one drink will relax you a certain amount, and that one valium would relax you a certain amount, you would expect that you should be able to predict the total amount of relaxation if you take one valium with a drink.  Unfortunately, this is not true.  Alcohol and valium are both in the class of drugs known as depressants.  When you combine two drugs from the same class, they enhance the effect of the other.  The alcohol would make the valium have a greater than expected result, and the valium would make the alcohol have a greater than expected result.  In this case 1 + 1 would not equal 2 as expected.  Instead it could equal 4 or 7.  Many accidental overdoses occur this way, some of them ending in death.

Mixing drugs from different classes has a different effect, but it can be equally dangerous.  For example, if you use too much cocaine and then drink, take a valium, or use heroin to "take the edge off," each drug will wear off at a different rate.  When the cocaine is gone, its countereffect on the heroin will also be gone, and the heroin will now exert its full effect.  It is hard to judge what quantity to use when under the effect of another drug (and with street drugs the quality/strength is unknown), and the full effect after the other drug has worn off could be overdose and death.

• Drug

• Psychoactive Drug

• Abuse

• Dependence

• Psychological Dependence

• Tolerance

• Withdrawal

• Cross Addiction

• Cross Dependence

• Cross Tolerance

• Synergism

Further Reading

(1).  Straight Facts About Drugs & Drug Abuse, Revised Edition, Health and Welfare Canada, copyright Minister of Supply and Services Canada, 1990

(2).  Drugs and Alcohol Behaviour: An Introduction to Behavioral Pharmacology, Second Edition, by William A. McKim, Memorial University of Newfoundland, Prentice Hall, 1991

(3)  Webster's Dictionary

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