Methadone is a potent synthetic opioid agonist which is well absorbed orally and has a long, although variable plasma half life. The effects of methadone are qualitatively similar to morphine and other opioids.
- Respiratory depression
- Euphoria (oral methadone causes less
- euphoria than intravenous heroin)
- Other Actions
- Decreased blood pressure
- Constriction of the pupils
- Gastrointestinal tract actions
- — Reduced gastric emptying
- — Reduced motility
- — Elevated pyloric sphincter tone
- — Elevated tone of Sphincter of Oddi
can result in biliary spasm
- Skin actions
— Histamine release
- Endocrine actions including
- — Reduced Follicle Stimulating
- — Reduced Luteinising Hormone
- — Elevated Prolactin
- — Reduced Adreno-Cortico-Trophic
- — Reduced testosterone
(Endocrine function may return to normal after 2-10 months on methadone)
- — Elevated Anti Diuretic Hormone
- Antitussive (cough suppressant)
Most people who have used heroin will experience few side effects from methadone. Once on a stable dose, tolerance develops until cognitive skills and attention are not impaired. Symptoms of constipation, sexual dysfunction and occasionally increased sweating can continue to be troubling for the duration of Methadone maintenance treatment.
Methadone is fat soluble and binds to a range of body tissues including the lungs, kidneys, liver and spleen such that the concentration of methadone in these organs is much higher than in blood. There is then a fairly slow transfer of methadone between these stores and the blood. Because of its good oral bioavailability and long half life, methadone is taken in an oral daily dose.
Methadone is primarily broken down in the liver via the cytochrome P450 enzyme system.
Approximately 10% of methadone administered orally is eliminated unchanged. The rest is metabolised and the (mainly inactive) metabolites are eliminated in the urine and faeces. Methadone is also secreted in sweat and saliva.
- Onset of effects:
- Peak effects: Approx 3 hours
Half life (in maintenance therapy)
: approx. 24 hours
- Time to reach stabilisation: 3-10 days
Source: Clinical Guidelines and Procedures for the Use of Methadone
in the Maintenance Treatment of
Authors: Sue Henry-Edwards, Linda Gowing, Jason White, Robert Ali, James Bell, Rodger Brough, Nick Lintzeris,
Alison Ritter & Allan Quigley