Effects of Chemicals: Overview

Side effects are unwanted but generally nondeleterious pharmacodynamic effects that occur alongside a drug's therapeutic action. Toxic effects are deleterious and classified as pharmacological, pathological, or genotoxic. For example, atropine causes dry mouth as a side effect, while toxic effects can cause severe damage or disease if prolonged or excessive.

Pharmacological toxic effects arise from excessive or prolonged drug usage and generally disappear as the drug is biotransformed or excreted, reducing its concentration in the body. In contrast, pathological and genotoxic effects may be repairable but can lead to cancer or death if severe, making them more persistent and potentially irreversible.

Side effects are unavoidable because they result from the same pharmacodynamic mechanism that produces the therapeutic effect. Drugs cannot selectively target only disease-related pathways; their chemical action affects multiple biological systems. This inherent property of drug action makes side effects an inevitable consequence of treatment.

Drugs are chemical substances obtained from three primary sources: natural sources such as plants and organisms, synthetic laboratory synthesis, and genetic engineering. These diverse sources provide the chemical compounds that, when administered to living bodies, produce various biological effects ranging from therapeutic to undesirable outcomes.

Pharmacological toxic effects generally disappear as the drug is biotransformed or excreted, reducing its concentration in the body. This process of drug metabolism and elimination naturally decreases the toxic effects over time. However, if exposure is severe or prolonged, additional intervention through enhanced elimination of poison may be necessary.

A therapeutic effect is the desirable outcome that treats or addresses a specific disease or health condition. All other effects experienced alongside the therapeutic effect are considered undesirable, including side effects and toxic effects. The primary objective of drug administration is to achieve the therapeutic effect while minimizing undesirable concurrent effects.

Genotoxic and pathological effects can be reversed in many instances, but if the effects are very severe, they may lead to serious health consequences including cancer or death. The reversibility depends on the extent of damage and the body's capacity to repair cellular or genetic harm caused by the drug exposure.