The mechanisms that make the movement of substances from blood vessels into brain cells more difficult than exchanges in other body organs, thus affording the brain greater protection from exposure to some substances found in the blood 

Blood-brain barrier

Humans have devised a variety of techniques for introducing substances into the body.
- ingestion 
- inhalation
- peripheral injection
- central injection

The routes of administration of drugs  

Collective name for all the factors that affect the movement of a drug into, through, and out of the body.

Bowdoin College

The amount of drug that reaches the brain and the speed with which is starts acting are determined in part by the drug's route of administration. 
- bioavailable
- biotransformation
- pharmacokinetics
- blood brain barrier

Drugs are administered and eliminated in many different ways

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

The process in which enzymes convert a drug into a metabolite that is itself active, possibly in ways that are substantially different from the actions of the original substance.

Biotransformation

Pharmacokinetics

Referring to a substance, usually a drug, that is present in the body in a form that is able to interact with physiological mechanisms.

Learn Before

Related

Learn After