The graph in this figure shows how different ways of taking a drug affect how much of the drug gets to the brain. The y-axis variable is the concentration of a drug in the brain and the x-axis is time after drug administration.
Drugs that are inhaled reach the brain quickly and at a high concentration. The drug remains in the brain for only a brief period of time before the concentration drops quickly.
A drug that is injected also reaches the brain quickly. It takes slightly more time to reach the brain than does inhaling a drug, but the drug’s concentration can be slightly greater than if the drug was inhaled. Like inhaled drugs, the concentration of an injected drug drops quickly.
A drug that is either snorted or snuffed does not reach the brain as quickly as a drug taken either by inhalation or injection. The maximum concentration that a snorted or snuffed drug reaches in the brain is lower than if the drug was inhaled or injected. The concentration of a snorted or snuffed drug in the brain rises more slowly and falls more slowly than that of inhaled or injected drugs.
A drug that is ingested takes much longer to reach the brain than if it is inhaled or injected, and longer even than if it is snorted or snuffed. Although the maximum concentration that the drug reaches in the brain is the lowest of any of the drug administration methods, an ingested drug remains in the brain longer than if the drug was taken by another method.