A number of animal studies and a small human pilot study have revealed that cannabinoids, extracts of cannabis legally sold as medical marijuana, could reduce cravings and ease withdrawal symptoms in heroin users. In light of the opioid epidemic in the United States, this is a neglected area of research that quickly needs attention, argues Yasmin L. Hurd, PhD, the Ward-Coleman Chair of Translational Neuroscience at the Icahn School of Medicine at Mount Sinai and Director of the Center for Addictive Disorders for the Mount Sinai Behavioral Health System. Dr. Hurd, who studies the molecular and neurochemical effects of both cannabinoids and opioids, discusses her position in a brief review published February 2 in Trends in Neuroscience.
While both cannabinoids and opioids regulate the perception of pain, the two drugs affect different parts of the brain and also affect how the sensation is communicated between neurons. For example, previous research shows that cannabinoids have a stronger effect on inflammation-based chronic pain, while opioids are particularly good at relieving acute pain. Problematically, opioids can quickly lead to a deadly addiction.
“If you look at both drugs and where their receptors are, opioids are much more dangerous in part because of the potential for overdose. The opioid receptors are very abundant in the brainstem area that regulates our respiration so they shut down the breathing center if opioid doses are high,” says Dr. Hurd. “Cannabinoids do not do that. They have a much wider window of therapeutic benefit without causing an overdose in adults. However, children have overdosed from consuming edible marijuana so that’s something to consider when making decisions regarding medical use.”
“Surprisingly, the scientific community has been largely missing from most conversations and policymaking decisions regarding the legalization of marijuana for medical purposes. Normally, preclinical models provide the foundation for clinical trials and then, after years of rigorous, structured scientific investigations, accrued evidence is evaluated by federal agencies to determine whether a particular compound should be approved for the treatment of specific symptoms/disease,” explains Dr. Hurd. “For marijuana, such a bar has not been met. Decisions across the country have been driven, in large part, by anecdotal reports and lobbying efforts by a growing marijuana industry. Despite the challenges of prescribing the medical use of a plant without the normal, rigorous clinical study process and within our existing clinical structure, specific constituents of the plant could be more easily developed for medical indications.”
Accumulating evidence suggests that cannabinoids could have long-lasting therapeutic effects. Preclinical animal models have long demonstrated that cannabidiol (CBD), a cannabinoid in the marijuana plant devoid of rewarding properties, reduces the rewarding properties of opioid drugs and withdrawal symptoms. Additionally, CBD directly reduces heroin-seeking behavior. A small pilot study in humans, led by Dr. Hurd, mirrored these animal findings. Dr. Hurd’s human study revealed that CBD reduced heroin-related, cue-induced craving experienced by heroin users. Moreover, CBD’s strongest effects were on the reduction of the anxiety induced by heroin cues.
Politicians are only beginning to acknowledge that an epidemic of opioid overdoses is taking place across the United States, particularly in suburban and rural areas, and the National Institute on Drug Abuse is asking researchers to think creatively about new strategies for pain relief. Marijuana has been a neglected option because there are restrictions on studying its effects in humans. While there has been a growing interest by the scientific community in cannabinoids since the legalization of medical marijuana, we still don’t know much about how it could be used therapeutically, despite at least a million people having been issued prescriptions.
“We have to be open to marijuana because there are components of the plant that seem to have therapeutic properties, but without empirical-based research or clinical trials, we’re letting anecdotes guide how people vote and how the policies are going to be made,” says Dr. Hurd. “For one of the first times in US history, it is the general public and politicians, not scientists and physicians, who are determining the medical value of this drug in states where marijuana use has been legalized for medical purposes. Clearly, the legalization of marijuana has outpaced the science. But if we want to be able to accurately say something is medical marijuana, we have to prove that it is, indeed, medicinal.”