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What is a drug?

The ancient Greeks believed drugs to be both poison and medicine. In modern society, a drug is whatever is ingested to treat any medical or psychological condition. Often what determines whether a substance is a drug is its manner of use. For example, alcohol is a beverage but it may be considered a drug if it is used for relaxation or to remove inhibitions. Similarly, it is used as a drug if it is taken to stimulate appetite.

Clinical definition of a drug

A drug is a therapeutic agent; any substance other than food, used in the prevention, diagnosis, alleviation, treatment or cure of disease in man or animals.

General definition of a drug

A drug is a substance other than food intended to affect the structure or function of a physiological system such as the human body.

Popular definition of a drug

The term drug refers mainly to chemical or plant-derived substances that affect psychological, behavioral or physical functions and lead to varying degrees of dependence or addiction.

Polydrug use

The taking of two or more drugs in combination either intentionally or inadvertently. For instance:

  • Alcohol interacts with barbiturates
  • Alcohol interacts with sedative hypnotics
  • Alcohol interacts with antihistamines
  • Amphetamine interacts with cocaine

Subjective Changes

Drug users may experiment with two different drugs to experience a range of effects simultaneously that neither drug could yield by itself. For instance:

LSD taken with an amphetamine would yield the amphetamine high in combination with the perceptual distortions of LSD.

Quantitative changes

These are the changes in the magnitude of the drug effect as a result of the drug combination. Quantitative effects are of two types:

  1. pharmacokinetic interference occurs when the presence of one drug in the body, or past exposure to it, influences the way the body handles a second drug;
  2. pharmocodynamic interference occurs when two or more drugs interact, causing a modified effect on body systems.

Several effects can be produced when two or more drugs are taken together. They are:

  1. Synergism, in which the action of one drug aids or enhances the action of another;
  2. Addition, in which the effects of two drugs are simply additive;
  3. Potentiation, in which there is a degree of synergism that is greater than additive;
  4. Antagonism, in which the pharmacological effect of one drug (agonist) is reduced by a second drug (antagonist). The second drug diminishes some or all of the expected effects of the first drug.

Any of the above drug interactions could result in death, depending upon the drugs involved.

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