Chapter 4 - Opioids

Summary

Heroin was first synthesized in the late 1800s and has proven to be one of the most addictive substances known to man. Prescription opioids, including morphine and oxycodone, also have high abuse potential; but until relatively recently, these agents were restricted mainly to palliative care and cancer patients. Now, however, prescription opioid use for the treatment of chronic noncancer pain has gained acceptance and become much more common. Correspondingly, misuse, abuse, and diversion of prescription opioids has increased dramatically and now far exceeds that of heroin. This has substantial consequences; thousands more Americans die each year from unintentional overdose with prescription opioids than from overdose with either heroin or cocaine. Opioid use disorder is therefore a significant public health concern. This chapter reviews the neurobiological effects of opioids as well as screening and management strategies for opioid use disorder.

Mu receptors in the VTA are critically involved in reinforcement and are also involved in drug dependence. Kappa receptors induce dysphoria, counteract mu receptors, and are involved in stress-related drug intake. Delta receptors are involved in emotional control.

Exogenous opioids are also thought to act at mu, delta, and kappa receptors, particularly mu receptors. Specifically, mu and possibly delta receptors in the VTA and the nucleus accumbens mediate the positive reinforcing properties of exogenous opioids.

If opioid misuse is suspected, a screening tool may be used for further assessment. There is no single accepted tool. Examples of self-report tools include the Current Opioid Misuse Measure and the Opioid Risk Tool. Examples of comprehensive tools include the Drug Abuse Screening Test, CAGE-AID, and UNCOPE.

It is also possible to manage patients undergoing withdrawal in an outpatient clinic or office. Clinicians in group or individual practices may provide naltrexone or, if they obtain a DEA DATA 2000 waiver, buprenorphine. Outpatient opioid treatment programs are also an option. These primarily offer methadone, although some may offer buprenorphine.

Individuals who have undergone withdrawal may have ongoing outpatient medication maintenance or may join a drug-free program, which does not provide opioid agonists but may provide naltrexone.

Methadone is orally active and can be administered once daily. The goal of methadone dosing is to suppress the patient's specific withdrawal symptoms and craving; thus, dosing is very individualized, but generally falls in the 40–100 mg/day range. Specifically, 40–60 mg/day is often sufficient to block opioid withdrawal symptoms, whereas higher doses are usually needed to block craving.