drug

A drug is any substance that, when introduced into a living organism, alters physical or mental function. In pharmacology, drugs are used to diagnose, prevent, or treat disease and disease-related conditions. They may be natural products, synthetic chemicals, or biologically derived molecules.

Drugs are categorized by their medical use or by their effects on the nervous system and other organ systems. Therapeutic drugs are prescribed to treat illness, while over-the-counter medicines are available without prescription. Recreational or illicit drugs refer to substances used outside or contrary to medical guidance. Substances may also be natural or synthetic.

Most drugs exert effects by interacting with specific molecular targets. Common mechanisms include receptor activation or blockade, enzyme inhibition, or interference with transport processes. Pharmacokinetics describes how the body absorbs, distributes, metabolizes, and eliminates a drug, influencing its onset, duration, and intensity of effect.

Safety and regulation govern drug development and use. Clinically, drugs undergo testing for safety and efficacy through trials before approval by regulatory authorities such as the Food and Drug Administration or the European Medicines Agency. After approval, post-market surveillance monitors adverse effects and interactions. Misuse can lead to harm, dependence, or legal penalties.

A well-functioning drug system emphasizes evidence-based therapy, informed consent, and ongoing monitoring. Advances in pharmacology have transformed medicine, yet challenges remain, including access, safety in diverse populations, and balancing innovation with public health priorities.