Drug

A drug was a general term for a form of medicine. Drugs could have many beneficial uses, they could be used to cure, treat and sedate. (TV: The Daleks, The Edge of Destruction) They could also be used recreationally like LSD and were often addictive like hashish and vraxoin. (PROSE: Dead Romance, TV: Marco Polo, Nightmare of Eden) A subsection of these recreational and often religious drugs were hallucinogenic drugs. (PROSE: The Left-Handed Hummingbird, Superior Beings)

As PhiCorp was in league with the Three Families and were aware of the oncoming "Miracle Day", they stocked up metanec for at least a year before the event to make a profit off of the public's great need for medication. (TV: Dead of Night)

Development
Many drugs that were in development were so new that their properties were unknown, only in combination could they function in a useful manner. (TV: Doctor Who and the Silurians) The Trees of Life on Tollip's World were reportedly capable of manufacturing a wide range of drugs and chemicals, including one with Hugo Tollip reckoned could give everlasting life. (PROSE: The Tree of Life)

Pharmaceutical companies regularly tested drugs' effectively, often on animal subjects, (PROSE: Warlock) but even sometimes on humans or other sentient species. (TV: Reset, New Earth)

Usage
Drugs could be ingested orally, (TV: Dead of Night) by injection, (TV: Children of Earth: Day Five, Rendition, PROSE: The Quantum Archangel) or by applying chemical patches to the skin. (TV: Gridlock)

Aside from medical or recreational uses, relaxant drugs could be used as the closest you'll ever get to a "truth drug" — they could break down some mental barriers, make people say things they normally wouldn't. (PROSE: Just War) Drugs could also be used to assist transformation (ie. into Cybermen) and mutation (ie. into Daleks). (TV: Attack of the Cybermen, AUDIO: The Time of the Daleks)

Addiction
Excessive use of drugs could lead to drug addiction, this was often the result of use of illicit drugs. (PROSE: Unnatural History, Wonderland) Victoria was at some point addicted to the fatal bubbleshake, but apparently got over it. (PROSE: Strange England)

In the 51st century, John Hart went to rehab for drugs, alcohol, sex and murder. (TV: Kiss Kiss, Bang Bang) The Terpsechians, on the other hand, thought drugs and alcohol good, and had no qualms against them in their society. (PROSE: The Glass Prison)

By the year 5,000,000,053, drugs were sold in New New York Undercity in the form of mood drugs, including Happy, Forget, Honesty and Sleep. When the Bliss drug became infected by a virus, killing everyone and everything outside the Motorway in seven minutes flat. When the Tenth Doctor arrived with Martha Jones, he shut down the dealers of Pharmacytown, where the moods were being sold. (TV: Gridlock)

The 456 used children as a form of recreational drug which they called "the hit". They therefore, in 2009, requested demanded one tenth of the children of Earth for this use. (TV: Children of Earth: Day Four)