 As a recreational drug, it is becoming more common to inhale ("Chasing the Dragon"), but, for medical purposes, intravenous (IV) injection is the most common method of administration.Morphine is subject to extensive first-pass metabolism (a large proportion is broken down in the liver), so, if taken orally, only 40% to 50% of the dose reaches the central nervous system.Resultant plasma levels after subcutaneous (SC), intramuscular (IM), and IV injection are all comparable.