Any substance which when absorbed into a living organism may modify one or more of its functions.
Comment: The term is generally accepted for a substance taken for a therapeutic purpose, but is also commonly used for substances of abuse. Just as any substance can be a toxicant, so any substance can be a drug. The term carries with it the implication of use for medical purposes, but also the potential for abuse to produce an effect desired by the abuser, but which is ultimately harmful.

The term "drug" was found in the following pages:

Researchers Urge the Removal of Mercury From Flu Shots | EVISA's News
Instrument database: Eksigent - ExpressHT™-Ultra HPLC system
FDA identifies no harmful effects to date with brain retention of gadolinium-based contrast agents for MRIs | EVISA's News
Journals database: Analusis
Link database: FDA: Questions & Answers: Apple Juice and Arsenic
Link database: Mercury in Medicine – Taking Unnecessary Risks
HPLC 2022: 52nd International Symposium on High Performance Liquid Phase Separation and Related Techniques | EVISA's Agenda of Events
Instrument database: Elemental Scientific Inc. (ESI) - SC-FIA Autosampler
Instrument database: Thermo Scientific - TSQ Quantum Ultra™ Triple Quadrupole Mass Spectrometer
Journals database: Cancer Detection and Prevention
Journals database: Biomedicines
Arsenic speciation in rice: a question of the rice plant species | EVISA's News
Journals database: International Journal of Nanomedicine
Journals database: Biopharmaceutics and Drug Disposition
Half of the rice sold in the UK breaches limits on arsenic for children | EVISA's News
Link database: Toxicology by Steven G. Gilbert: A Small Dose of Arsenic
11th International Symposium on the Synthesis and Applications of Isotopes and Isotopically Labelled Compounds | EVISA's Agenda of Events
Journals database: ChemMedChem
Journals database: Current Pharmaceutical Analysis
Link database: Hong Kong: Open Laboratory of Chemical Biology: C.-M. Che (HKU)