Final answer:
The onset of action is the time it takes for a drug to start producing its effects in the body. The slowest route of administration is oral, while the fastest is intravenous.
Step-by-step explanation:
The onset of action refers to the time it takes for a drug to start producing its effects in the body. It can vary depending on the route of administration, which refers to the way the drug is introduced into the body. The slowest route of administration is oral, where the drug is taken by mouth and has to be absorbed through the digestive system before it can reach the bloodstream. The fastest route of administration is intravenous, where the drug is directly injected into a vein, allowing it to quickly enter the bloodstream.