Updated: Aug 23
Opioid Receptors and The Reward Pathway
To understand what Naltrexone is, and why it is prescribed, it is first important to know about mμ opioid receptors and the reward pathway. The opioid system controls pain, reward and addictive behaviours. Opioids exert their effects through three opioid receptors or targets of action, mμ, delta and kappa. Opioid receptors in the brain can be activated naturally by substances made in the body, like enkephalins, dynorphins and endorphins, which are released by neurons or nerve cells. The same opioid receptors can also be activated by external substances, like alcohol, morphine, pethidine, tramadol, oxycodone, heroin, dextropropoxyphene and other synthetic opioid compounds. These substances are not only potent pain killers, but are also highly addictive.
This is because mμ opioid receptors are abundant in the the reward pathway of the brain. This is a pathway that makes us want to do something again, and again. In nature, whenever we perform activities that help us prolong our lives or reproduce, this pathway is activated, giving us intense pleasure. For example, this pathway is activated when you exercise, eat delicious food, or have sexual intercourse.
Alcohol and opioid drugs like heroin activate this pathway artificially, and much more strongly than it normally would be, giving you intense pleasure the first few times. However, after the few times, the receptors in the reward pathway respond lesser and lesser to the drugs and even natural stimuli, so much so that without the drugs, you find no pleasure in anything in life other than the drugs you take. This is why most addicts are so malnourished and demotivated, and have a characteristic empty gaze.
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What Is Naltrexone?
Naltrexone is an opioid receptor antagonist (meaning it blocks those receptors) with highest affinity for the mμ opioid receptor. Naltrexone blocks the effects of alcohol, opioid drugs, and even cannabis and behavioural addictions. Craving decreases substantially in those people on naltrexone, and that this craving reduction occurs very quickly, from the beginning of treatment (first 2-3 weeks) and doesn’t seem to return after that. There are certainly people who continue to have cravings, but this is a rather small proportion and usually occurs only after coming off medication. Those who maintain treatment with naltrexone have minimal to no cravings.
What Is A Naltrexone Implant?
A Naltrexone implant is an extended release formulation for patients who are likely to skip oral medicines, and have uncontrollable and severe addiction. Naltrexone implants in India are currently available in a 765mg dose, which lasts upto 3 months, although research is being done on 6 month and 1 year lasting implants too.
What Are The Steps To Be Taken Before Naltrexone Implantation?
To prevent occurrence of an acute abstinence syndrome (withdrawal) in patients dependent on opioids, or exacerbation of a pre-existing subclinical abstinence syndrome, opioid-dependent patients, including those being treated for alcohol dependence, must be opioid-free for a minimum of 7–10 days before starting Naltrexone Implant treatment. It is for this reason that patients are admitted to a high quality de-addiction facility for a minimum of 20 days, during which the detoxification process is completed accompanied by a full panel of investigations first, and then an oral dose of Naltrexone is then given to the patient for a week, before the implant can be administered.
Does Naltrexone Implantation Have Any Side Effects?
In most cases, Naltrexone implantation will have no side effects whatsoever. Naltrexone may occasionally cause an allergic reaction. This can be easily ruled out during the oral challenge to Naltrexone. Less serious side effects may include: feeling anxious, nervous, restless, or irritable, increased thirst, muscle or joint aches, weakness or tiredness, sleep problems (insomnia), decreased sex drive, impotence, or difficulty having an orgasm.
Call your doctor at once if you have any of these serious side effects: blurred vision or eye problems, fast heartbeat, wheezing, difficulty breathing, mood changes, hallucinations (seeing or hearing things), confusion, thoughts of hurting yourself, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes), ear pain, ringing in your ears, feeling light-headed, fainting, Skin rash or itching, pain, redness, bruising, itching, swelling, oozing, skin changes, or a hard lump where the medication was implanted.