I decided to make this FAQ to be a companion to the buprenorphine FAQ phrozen created. With these two FAQ's, anyone considering some for of opioid maintenance will have two resources to use to compare and contrast the differences of the two drugs, helping them come to a decision of which drug would be better for them.
Some of the information contained in the FAQ was not authored by me. I have listed all the sources used at the bottom of the post.
What is it?
Merck methadone information
Methadone is a full mu-opioid agonist. Methadone also binds to the glutamatergic NMDA (N-methyl-D-aspartate) receptor, and thus acts as a receptor antagonist against glutamate . NMDA antagonists such as dextromethorphan, ketamine, and ibogaine are being studied for their role in decreasing the development of tolerance to opioids and as possible for eliminating addiction/tolerance/withdrawal, possibly by disrupting memory circuitry. Acting as an NMDA antagonist may be one mechanism by which methadone decreases craving for opioids and tolerance .
Methadone, a long-acting synthetic narcotic analgesic, was first used in the maintenance treatment of drug addiction in the mid-1960s by Drs. Vincent Dole and Marie Nyswander of Rockefeller University. There are now 115,000 methadone maintenance patients in the United States, 40,000 of whom are in New York State and about half that many are in California .
What is a normal dose?
There really is no normal dose. The dose required for maintenance therapy is highly dependent upon the dose of whatever other opiate you were using before getting on methadone. However, most clinics normally start you at a dose between 40mg and 60mg, and increase by 5mg or 10mg every day or two until you get to the required dose.
The most common and traditional dosing regimens, however, tend to fall far short of providing optimum or even sufficient results for a number of patients. This is due to the ceilings many clinics place on dose levels .
What are the withdrawals like?
The withdrawals from methadone are similar to every other opiate, although they have been reported to be much more severe if the dose is too high when the patient cuts off usage. Physical symptoms include nausea, sneezing, vomiting, diarrhea, sweats, chills, joint pain, elevated blood pressure, fever, runny nose, and increased tear production.
The psychological symptoms can include depression, anxiety, paranoia, panic disorders, delusions, decreased sex drive, prolonged insomnia, and fatigue or exhaustion.
Is there a ceiling dose?
No. Your dose of methadone can be increased as high as it needs to go. One thing to consider when that starts to happen is maybe entering a detox program to get your dose back down and possibly even taper off of it completely.
What is methadones bioavailability?
The bioavailability is between 40 - 80%, with a half life of 24 - 36 hours . The Wikipedia article has it listed as 40 - 90%, and more than one other source, including Bluelights own thread on bioavailability, have put it closer to 80 - 90%.
- Methadone is Schedule II in the US.
- It is metabolized by the enzymes CYP3A4, CYP2B6 and CYP2D6 
- Half-life: 24 - 36 hours
- Drug Test: Not detected in standard 5-panel test, but can be tested for.
1, 2 - Wikipedia Article on Methadone - Mode of Action
3 - Methadone Maintenance Treatment
4 - Wikipedia Article on Methadone - Dosage
5 - ChemistryDaily.com Encyclopedia Entry on Methadone
6 - Wikipedia Article on Methadone - Pharmacology