MEDICATED ASSISTED THERAPY

Methadone

FULL AGONIST

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Like heroin, methadone fully occupies and activates the mu opioid receptor (see box on the right). However, there are significant differences between heroin and methadone, for example: heroin gives a peak “rush” and has a fairly rapid metabolism (4-5 hours) resulting in extreme highs and lows. Methadone occupies the mu-opioid receptors without offering an initial “rush” and is metabolized very slowly, up to 36 hours. This allows for a stabilization of the patient seeking recovery from heroin addiction because, a) the opioid receptors are occupied so heroin, if introduced, would not have a receptor to bind to and, b) because the receptors are activated at a consistent level, the person suffering from opioid addiction can resume normal functioning without withdrawal symptoms or the intense craving for heroin. Methadone is a full agonist because it occupies and fully activates the receptor (see box).

Naltrexone, Naloxone

ANTAGONISTS

Antagonists occupy the mu opioid receptor but do not activate it (see box on right). Because they occupy the same receptors as opioids seeks, if the person recovering from opioid addiction uses heroin/opioids, the opioids have no receptors to bind to, thus, the individual does not get the sought for “reward.” Antagonist medications include naltrexone, vivitrol, nalmefene and naloxone. Naloxone is short-acting and, therefore, is not used in MAT (except as noted below, “Suboxone: what is it?”). Naltrexone can be administered via daily tablets, monthly injections (vivitrol), and implants, whose effects last up to 6 months.

Buprenorphine

PARTIAL AGONIST

The buprenorphine based medications such as Suboxone and Subutex used in MAT are partial agonists (see box on right). Since buprenorphine partially activates the opioid receptor, it helps to reduce intense heroin/opioid cravings; and because it occupies the same receptors as heroin seeks, if heroin/opioids are used, they have no receptors to bind to and the sought for “reward” is not achieved.

Want to know more about how Suboxone works? See below.