The fastest among intramuscular, intravenous and oral medications is intravenous. In Intravenous mediation, the administered drug goes directly into the vein thereby coming in direct contact with the blood, which transports it to its required destination bringing about an immediate correcting or reactivation of worn-out cell(s) as the case may be.

It is taken as drips where the patient is allowed to maintain a particular position for a longer period compared to intramuscular. So it's more effective in relieving pain, though it also has tremendous disadvantages.