The 4 Effects

The 4 Effects

These four effects address the ways in which two, or more, categories of drugs affect a single sign or symptom.

Overlapping Effect

This effect involves one drug which has an effect on a particular sign or symptom and a second drug which does not have an effect on that sign or symptom. This can be mathematically expressed as one plus zero equals one (1 + 0 = 1).

Antagonistic Effect

This effect involves two drugs that have the opposite effect on a specific sign or symptom. This can be mathematically expressed as one minus one equals zero (1 - 1 = 0).

Additive Effect

This effect is where both drugs have the same effect on a specific sign or symptom. This can be mathematically expressed as one plus one equals two (1 + 1 = 2).

Null Effect

This effect is where neither drug has an effect on the sign or symptom. This can be mathematically expressed as zero plus zero equals zero (0 + 0 = 0).

Example of Overlapping Effect

An example is PCP and a CNS Stimulant, cocaine, as they affect HGN. PCP causes HGN and cocaine does not induce or cause HGN, therefore when under the influence of the combination of these drugs, the subject will display HGN.

Example of Null Effect

An example is a Central Nervous System (CNS) Stimulant, cocaine, and a Narcotic Analgesic, Heroin, as they affect Horizontal Gaze Nystagmus (HGN). Neither drug causes HGN, therefore when under the influence of the combination of these drugs, the subject will not display HGN.

Example of Additive Effect

An example would be a CNS Depressant, Thorazine, and a Narcotic Analgesic, Heroin, as they affect pulse. Both Thorazine and Heroin lower pulse rate, therefore a subject under the influence of a combination of these drugs will have a lowered pulse rate. Since both drug categories lower pulse rate, their combination may result in a pulse so low, 30-40 beats per minute, as to be medically dangerous.

Example of Antagonistic Effect

An example would be a Narcotic Analgesic, Heroin, and a Central Nervous System Stimulant, cocaine, as they affect pupil size. The heroin will constrict the pupil and the cocaine will dilate the pupil, therefore a subject under the influence of a combination of these drugs may exhibit pupils that range from constricted to dilated.

The range from constricted to dilated

CONSTRICTED NORMAL DIALATED