TUESDAY, May 19, 2026 (HealthDay News) — Adding a synthetic weed-derived drug to opioid painkillers brings no relief to people with excruciating knee pain, a new study says.

Neither the cannabis drug dronabinol nor the opioid hydromorphone alone provided significant pain relief for people with knee arthritis, and combining them did not improve results, researchers reported recently in the journal Anesthesiology.

“Some patients believe combining cannabis with opioids can help with pain, and clinicians may recommend or prescribe it in states where cannabis is legal,” said lead researcher Katrina Hamilton, an experimental psychologist at Ohio University in Athens.

“Our study suggests that isn’t the case and patients may experience more side effects when the drugs are combined,” Hamilton said in a news release.

Dronabinol is a man-made form of tetrahydrocannabinol (THC), the chemical compound in weed that produces intoxication, according to Drugs.com.

For the new study, researchers recruited 21 patients with knee arthritis. Each person took part in four sessions in which they were given different combinations of pills:

Hydromorphone and a placebo
Dronabinol and a placebo
Dronabinol and hydromorphone
Two placebo pills

After taking the pills, the patients underwent tests to see how the drugs affected pain.

Results showed that opioids and cannabis, either alone or together, did not provide robust relief for knee pain. Further, opioids reduced pain sensitivity but did not meaningfully reduce participants’ self-reported pain. Cannabis didn’t appear to help at all.

There was no added pain relief when the two drugs were combined, but there were stronger and more noticeable side effects like drowsiness, dizziness and impaired thinking, researchers said.

However, researchers noted that these results might not fully represent how people use weed in real-world situations.

“In the real world, people often use cannabis differently, including lower starting doses, using gradually stronger doses, which may affect both benefits and side effects,” Hamilton said. “More research is needed to better understand how cannabis affects pain when used in real-world settings.”

More information

Harvard Medical School has more on controlling knee pain.

SOURCE: American Society of Anesthesiologists, news release, April 20, 2026

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