At some point, after a drug is introduced into the body, it will reach a peak concentration. The drug concentration will then start to decrease as the drug is eliminated. The figure on the right shows a typical drug kinetic when a drug is given intravenously (IV). Different routes of administering medications lead to different kinetics. Inhalation and IV infusion have very fast-onset, while oral medications or transdermal drug delivery is much slower. The elimination time will also be affected by the absorption time (see second figure).
| Route | Onset Time |
| Intravenous (IV) | <60 seconds |
| Inhalation | <2 min |
| Sublingual | 3-4 minutes |
| Intramuscular (IM) | 3-4 minutes |
| Subcutaneous | 15-30 minutes |
| Rectal | 5-30 minutes |
| Ingestion | 3-90 minutes |
| Transdermal patch | ~12 hours |
