a. Something that has been purified.
b. Something that causes a characteristic change in an organism.
or c. Something that is chosen because it might cause a characteristic change.
Once a drug has been identified, there are some questions to ask:
- What are its side effects?
- How small of an amount can have an effect?
- Does it interact with anything else?
- Does chronic use of it cause problems? At what levels? What problems?
- Does its usage affect other organisms?
- What do you need to do to stop using it safely?
- Can it cause acute harmful effects? At what levels? What effects?
A key point of this definition is that it does not specify that a drug must be a substance. Also a drug is defined by the change, not by its design.
I’ll come back to this definition once in a while to show how it can be a useful frame to think about important issues.