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Opioids Blockade and Naltrexone Implants

Naltrexone Implants and Prolonged-Release Buprenorphine Injections are medications used to block opioid receptors in opioid dependent patients. Both can block the effects of morphine, heroin, codeine, oxycodone, methadone (Physeptone) and others.

Naltrexone is an opioid antagonist (it blocks opioids receptors) and buprenorphine is a partial agonist that binds strongly to opioid receptors and exert some opioid effects but does not produce a high or mood alteration.

How do opioid blockers work?

They enter the brain and nervous system and bind to opioid receptors. For opioids to produce their effects, they must bind to the same opioid receptors, but naltrexone and buprenorphine (at appropriate dose) stop opioids getting to them for up to three days after an oral dose.

These receptors are part of the complex reward mechanisms that motivate us and lead to repetitive behaviour. If the reward is blocked, the cravings and addictive behaviours reduce and new ones reassert themselves with time. These medications help with relapse prevention.

At The OAD Clinic we offer treatment with oral naltrexone and Buvidal (prolonged-release buprenorphine injection) to prevent opiate relapse. These medications are prescribed after the body has been fully detoxified from opiates, otherwise strong withdrawal symptoms may be experienced. It is part of our comprehensive opiate addiction treatment programme that includes counselling, monitoring and lifestyle changes.

Learn more about Buvidal injection


Naltrexone Implants

Naltrexone implants are specially formulated, sterilised pellets containing 1000 mg of Naltrexone that your doctor will insert under the skin (usually of your abdomen) during a minor surgical procedure. Its effect normally lasts for 10 to 12 weeks. Over time, the implant is completely absorbed in your body and does not need to be removed. Naltrexone Implants do not have a product licence in the UK and are still regarded as experimental.


Important considerations

Although Naltrexone implants have been used for many years in Australia and in some clinics across Europe, they are not licensed medications in the UK. Here, they can only be used in a limited number of cases and as part of approved research projects.

There is an ongoing clinical study supported by the National Institute on Drug Abuse and New York State Psychiatric Institute on utilizing Naltrexone Implants produced in Australia.

Basically, Naltrexone Implants are still under research (i).


Naltrexone Implants Complications and Side Effects

There are two types of side effects, one related to the surgical insertion, and second related to naltrexone itself. The most common complication is infections. These result from contamination during the surgical procedure and inappropriate wound care.


Another but less frequent complication, is an allergic reaction to certain chemicals contained in the naltrexone pellets.  Allergic reactions start with inflammation of the tissue under the wound and can progress to expulsion of pellets, infection and even abscess that has to be drained. In this case, the pellets have to be surgically removed.


There is no consistency in the manufacturing of the different implants available on the market, and some of them break up instead of dissolving over time. When the pellets break up, they release a great amount of naltrexone in the system resulting in acute opioid withdrawal symptoms. When this happens, the implant has to be surgically removed without delay. Unfortunately, we have had to do this for some patients who had naltrexone implants abroad.


Another factor to be carefully considered is patient selection. Some people are pressured by their families to have an implant, but once inserted they cannot cope with the side effects and request it to be removed. In extreme cases people try to remove it themselves, with very unpleasant results.

Side effects related to naltrexone can be very upsetting for some patients.

These include: nausea, headaches, dizziness, tiredness, trouble sleeping, mild or moderate opioid withdrawal symptoms such as abdominal cramps, restlessness, bone and muscle aches.

Some people also complain of “flat mood” and lack of motivation.

It is worth mentioning that once patients have finished naltrexone treatment, they lose all previous tolerance to opioids and therefore at high risk overdose should they decide to use opioids again.


At The OAD Clinic we offer a safe opioid blocker with Buvidal (prolonged-release buprenorphine injection).

Sublingual tablets can be effective, but only as long as you take them every day. However, once a depo injection has been administered, its effect will last a month or even longer, protecting the patient from opioid cravings.

Currently we do not offer Naltrexone Implants for several reasons:

First, because they are not licensed for human use in the UK. Also, they need a minor surgical procedure followed by close monitoring for potential complications such us wound infection, implant rejection, allergic reactions or intense patient discomfort. This can be a problem for people living outside the clinic catchment area, who either have to make their own arrangements or do not attend follow up procedures at all, resulting in complications.

Naltrexone implants keep patients free of opioids, but relapse can be very dangerous due to loss of tolerance. On the other hand, prolonged-release buprenorphine injections provide a partial opioid agonist that does not alter mood or create a high. It safely blocks opioid receptors and removes overdose risks.

When patients are ready to stop their injections, they usually don’t need any further treatment because the rate of buprenorphine dose reduction is very gradual and comfortable and withdrawal symptoms rarely present.


Please do not hesitate to contact us for any further information or to book an appointment.


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