Morphine can be taken in many ways, either orally, subcutaneously, intravenously, rectally, intrathecally or epidurally. It is more usual to be inhaled on the streets, the so called “chasing the dragon”. Of course, for medicinal purposes, morphine is usually administrated intravenously. When taken orally, a large proportion is broken down in the liver, so only 40-50% of the dose reaches the central nervous system.

Resultant plasma levels after subcutaneous (SC), intramuscular (IM), and intravenously (IV) injection are all comparable. After IM or SC injections, morphine plasma levels peak in approximately 20 minutes, and after oral administration levels peak in approximately 30 minutes.

Morphine is metabolised primarily in the liver and approximately 87% of a dose of morphine is excreted in the urine within 72 hours of administration. Morphine is primarily metabolized into morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) via glucuronidation by phase II metabolism enzyme UDP-glucuronosyl transferase-2B7 (UGT2B7).

About 60% of morphine is converted to M3G, and 6–10% is converted to M6G. The cytochrome P450 (CYP) family of enzymes involved in phase I metabolism plays a lesser role. Not only does the metabolism occur in the liver but it may also take place in the brain and the kidneys. M3G does not undergo opioid receptor binding and has no analgesic effect. M6G binds to mu-receptors and is a more potent analgesic than morphine.

Morphine may also be metabolized into small amounts of normorphine, codeine, and hydromorphone. Metabolism rate is determined by gender, age, diet, genetic makeup, disease state (if any) and use of other medications. The elimination half-life of morphine is approximately 120 minutes, though there may be slight differences between men and women.

Morphine can be stored in fat, and thus can be detectable even after death. Morphine is able to cross the blood-brain barrier but because of poor lipid solubility, protein binding, rapid conjugation with glucuronic acid and ionization, it does not cross easily. Diacetylmorphine, which is derived from morphine, crosses the blood-brain barrier more easily, making it more potent.

We strongly recommend to everyone reading this article to stay out of morphine abuse, however, if you or someone close to you have problems with morphine addiction, we suggest you to visit Drug Rehab Services.