Naltrexone - Adverse Effects

Adverse Effects

The most common side effects reported with naltrexone are non-specific gastrointestinal complaints such as diarrhea and abdominal cramping.

Naltrexone has been reported to cause liver damage (when given at doses higher than recommended). It carries an FDA boxed warning for this rare side effect. Due to these reports, some physicians may check liver function tests prior to starting naltrexone, and periodically thereafter. Concerns for liver toxicity initially arose from a study of non-addicted obese patients receiving 300mg of naltrexone.Subsequent studies have suggested limited toxicity in other patient populations.

Naltrexone should not be started prior to several (typically 7-10) days of abstinence from opioids. This is due to the risk of acute opioid withdrawal if naltrexone is taken, as naltrexone will displace most opioids from their receptors. The time of abstinence may be shorter than 7 days, depending on the half-life of the specific opioid taken. Some physicians use a naloxone challenge to determine whether an individual has any opioids remaining. The challenge involves giving a test dose of naloxone and monitoring for opioid withdrawal. If withdrawal occurs, naltrexone should not be started.

It is important that one not attempt to use opioids while using naltrexone. Although naltrexone blocks the opioid receptor, it is possible to override this blockade with very high doses of opioids. However this is quite dangerous and may lead to opioid overdose, respiratory depression, and death. Similarly one will not show normal response to opioid pain medications when taking naltrexone. In a supervised medical setting pain relief is possible but may require higher than usual doses, and the individual should be closely monitored for respiratory depression. All individuals taking naltrexone are encouraged to keep a card or a note in their wallet in case of an injury or another medical emergency. This is to let medical personnel know that special procedures are required if opiate-based painkillers are to be used.

There has been some controversy regarding the use of opioid-receptor antagonists, such as naltrexone, in the long-term management of opioid dependence due to the effect of these agents in sensitizing the opioid receptors. That is, after therapy, the opioid receptors continue to have increased sensitivity for a period during which the patient is at increased risk of opioid overdose. This effect reinforces the necessity of monitoring of therapy and provision of patient support measures by medical practitioners.