By Pat Anson, PNN Editor

Many doctors who prescribe opioids to pain patients tell them not to mix opioids with cannabis – fearing a combination of the two could raise the risk of addiction and overdose. Some doctors will stop prescribing opioids to patients or even discharge them if cannabis is detected in their drug tests.

But a new animal study suggests that cannabidiol (CBD) and tetrahydrocannabinol (THC) – the active ingredients in marijuana – may actually be safe to use with opioids and could be an effective way to lower opioid doses while still providing pain relief. 

“There is intense interest in using medical marijuana in patients with chronic pain because compounds in marijuana like CBD and THC may produce pain relief themselves or enhance the pain-relieving effects of opioids,” said Lawrence Carey, PhD, a postdoctoral fellow at the University of Texas Health Science Center, San Antonio. “This means people could potentially use lower doses of opioids and still get relief from pain. Taking less pain medication could also lead to a lowered risk of addiction or physical dependence to opioids.”

Carey and his colleagues tested their theory by giving rhesus monkeys dependent on opioids various doses of CBD and THC, either alone or together. The monkeys were then given opportunities to press levers that either gave them a food reward or an injection of fentanyl, a potent synthetic opioid.

Their findings, presented this week at the annual meeting of the American Society for Pharmacology and Experimental Therapeutics, showed that CBD and THC did not increase or decrease the number of times the primates selected fentanyl over food. This suggests that cannabis does not enhance the rewarding effects of opioids or raise the risk of addiction, at least for rhesus monkeys.

“Giving the animals the opportunity to choose between a drug injection and a food reward helped us to somewhat replicate choices a human drug user may face, such as whether to spend money on drugs or food,” Carey said in a press release. “Having the option of responding for food is also useful for studying drugs like THC that produce sedative effects. It helps demonstrate the animal is reallocating behavior from drug to food choice instead of simply shutting down response for a drug due to sedation.”

Carey says more studies on humans are needed to determine whether THC and CBD are safe to use with opioids, and if they work well together.

A 2020 study of patients prescribed opioids for chronic low back pain found that half were able to stop using opioids after starting cannabis therapy, but it took an average of six years to do so. About 15% reduced their use of opioids and the remainder either kept taking the same amount or increased their opioid use.

Carey is now conducting animal studies to assess whether CBD and THC can decrease symptoms of opioid withdrawal. 

“A big reason why people continue to take opioids after they become addicted is the appearance of withdrawal symptoms,” said Carey. “We are using what we learned from this study to determine whether these doses — which didn’t alter choice for food or drug rewards — may help relieve opioid withdrawal or decrease relapse and drug seeking behavior following periods of abstinence.”