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 as seen in Table 1. The elimination time will also be affected by the absorption time (see second figure).
Table 1. Route and Corresponding Onset Time.| 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 |
