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Buprenorphine Bound Receptors are Stable in the Presence of Both Morphine and Naloxone.


Full agonist

Activation zone

Partial Agonists​: are drugs that occupy the mu opioid receptors and partially activate them. They contain buprenorphine and include, suboxone, subutex....

Read more about heroin, addiction and the brain




​Full Agonist

Classes of Medications for Heroin Addiction

Naltrexone occupies the mu opioid receptor but does not activate it. It is an "Antagonist" ​(see box). Because it occupies the same receptors as heroin 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 not used in MAT except as noted below). Vivitrol is a timed release form of naltrexone and is taken by injection every 30 days, whereas naltrexone tablets are taken daily. Since antagonist medications do not activate the receptors, for some individuals recovering from opioid addiction, cravings for heroin/opioids may not be adequately managed by these medications.


NALTREXONE: Naltrexone is an antagonist. It is used in MAT to block the opioid receptors so that heroin cannot reach its target. It is taken by tablet daily, or in the form of a time released injection (Vivitrol) every 30 days.

NALOXONE: Naloxone is an antagoinist. It is commonly known as "Narcan."  It is NOT used in MAT because it is very short acting (30-70 minutes). However, because of it's affinity for the opioid receptors when injected, it can immediately rescue the patient from an opioid overdose by stripping the opioid from its receptor, thus, reversing an overdose. 

SUBOXONE: The active ingredient in Suboxone is the partial agonist, buprenorphine. However it also contains the antagonist drug Naloxone (Narcan). The Naloxone is added for the sole purpose of reducing the incidence of abuse. When suboxone is taken as prescribed (by mouth), the buprenorphine will reach the opioid receptors first and narcan (naloxone) will not be able to displace it because  buprenorphine binds tightly to the opioid receptor (see box, right). However, if the patient attempts to inject the suboxone hoping for a buprenorphine "high," the narcan will more immediately occupy the receptors, blocking the buprenorphine effects.

Buprenorphine sits snugly in the mu receptor and partially stimulates it. For this reason, it is considered a partial agonist. Neither morphine (heroin) nor naloxone (narcan) can displace buprenorphine from the receptor once it is bound. Therefore, heroin, if used when buprenorphine is bound, will not give the desired effect to the patient. Important to note, though buprenorphine overdose is rare, naloxone will likely not reverse a buprenorphine overdose.



Partial Agonist


Partial agonist


Suboxone: What is It?

​​​History of Methadone-Assisted Therapy for Heroin Addiction

Suboxone, Naloxone and Naltrexone Confusion



Methadone Maintenance Treatment is the gold standard that newer medications for treatment of heroin addiction are being compared to. It has been evaluated since its development in 1964 with consistent results: reduced heroin use, reduced death rates, and it allows patients to improve health and social productivity. Most of the more current studies with methadone in connection with heroin addiction recovery are done in an effort to analyze effective dosages and or compare with newer medication alternatives.


To answer this question, let’s first look how heroin and methadone affect the brain. Heroin and methadone both function by occupying the mu-opioid receptors in the brain. They are called "full agonists(see box) because not only do they occupy the receptors, but they activate them as well. However, there are significant differences between heroin and methadone: heroin gives a peak “rush” and has a fairly rapid metabolism (4-5 hours) resulting in extreme highs and lows for the addict. 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. If methadone and heroin both occupy and activate the same receptors, some feel that using methadone to treat heroin addiction is “trading one drug for another.” All reputable Heroin Recovery sources including (NIDA) The National Institute on Drug Abuse, and SAMSHA admonish against this notion as, currently, it is the best way to keep sufferers from SUD (substance use disorder), alive long enough to successfully employ other treatment methods.

Partially Activated mu receptor

Buprenorphine            Naloxone                    Suboxone

un-Occupied, Non-Activated mu receptor

Naloxone bound receptor



Full Agonists​: are drugs that occupy the mu opioid receptors  and fully activate them. They include opioids such as morphine, methadone, heroin...

naloxone is not used in MAT because it is short-acting. However because of its immediate bonding to (and ability to remove heroin from) the opioid receptor upon injection, it is used to rescue heroin overdoses. 



Fully Activated 

mu receptor


There are different types of medication used for heroin addiction recovery. All bind to the opioid receptor but have different effects. Methadone has, by far, the longest treatment history with a wealth of clinical studies, research, and meta-analyses.

Buprenorphine vs Morphine and Naloxone*


 Medication: Action on the Opioid Receptor 

Antagonists​: are drugs that occupy the mu opioid receptors but do not activate them. They include vivitrol, naltrexone, naloxone... 

Buprenorphine bound receptor

Occupied Non-Activated mu receptor


The buprenorphine based medications such as Suboxone and Subutex used in MAT are "partial agonists" (see box). Since buprenorphine partially activates the mu receptor, it helps to reduce intense heroin cravings; and because it occupies the same receptors as heroin seeks, if heroin is used, it has no receptors to bind to. The sought for “reward” is not achieved. For some people recovering from opioid addiction, buprenorphine may not reduce cravings enough to avoid relapse. However, this is the preferred medication used in MAT as methadone has a higher incidence of overdose when misused; it is rare that someone can overdose from buprenorphine misuse because of how it is administered (see box below: "Suboxone, Naloxone and Naltrexone confusion" ).

Why Does Methadone Work

Suboxone is buprenorphine with naloxone (narcan). Both naloxone and buprenorphine fit snugly in the opioid receptor; once bound to the receptor neither can compete the other out. When used as prescribed (ingested), buprenorphine acts quickly to occupy the opioid receptors, thereby achieving its therapeutic purpose. However, if the patient hopes for a stronger rush and attempts to inject suboxone, the very fast acting injected Narcan (used to reverse heroin overdoses) will quickly bind to the receptors and buprenorphine will be unable to act. 


Medication-Assisted Therapy for Heroin Addiction Recovery


* See box (left):  "Suboxone, Naloxone and Naltrexone Confusion"

This schema is a simplistic modeling of how the various classes of medications act on the mu-opioid receptors.