Short answers, pulled from the story.
A drug is any chemical substance other than a nutrient or essential dietary ingredient that produces a biological effect when administered to a living organism. Drugs can be taken by inhalation, injection, smoking, ingestion, absorption through a skin patch, suppository, or dissolution under the tongue.
A pharmaceutical drug, also called a medication or medicine, is a chemical substance used to treat, cure, prevent, or diagnose a disease or to promote well-being. Traditionally drugs were obtained by extraction from medicinal plants, and more recently also through organic synthesis.
Pharmaceutical drugs are sorted into drug classes that share a similar chemical structure, mechanism of action, mode of action, or target disease. The Anatomical Therapeutic Chemical Classification System, or ATC, is the most widely used system, while the Biopharmaceutics Classification System sorts drugs by solubility and permeability or absorption.
Drug action is highly specific and often depends on the patient's genotype, so the 10 highest-grossing drugs in the United States may help only 4 to 25 percent of people. Erbitux improves survival in colorectal cancer patients with a particular EGFR gene mutation, and vemurafenib is used for melanoma patients with a BRAF gene mutation.
Entheogens are drugs, mostly hallucinogens, used as the basis of some ethnic religions, and the word means generating the divine within. Shamans use them to achieve religious ecstasy, including Amazonian shamans who use ayahuasca and Mazatec shamans who use Salvia divinorum.
The Single Convention on Narcotic Drugs, an international treaty brought about in 1961, prohibits the use of narcotics except for medical research and treatment. In 1971 the Convention on Psychotropic Substances was introduced to address newer recreational psychoactive and psychedelic drugs.
Nootropics, commonly called smart drugs, are claimed to improve cognitive abilities such as memory, concentration, and learning, and include methylphenidate branded as Ritalin. Designer drugs are produced or altered substances, an early example being LSD synthesized from ergot, with others including designer steroids and synthetic cannabinoids.