TUCUMÁN, Argentina — Although further research is needed, fibromyalgia and osteoarthritis are emerging as the two rheumatologic conditions with the strongest evidence supporting medical cannabis as a potentially valuable therapeutic option, experts agreed during a panel at the 58th Argentine Congress of Rheumatology, held from October 8 to 11.

“The current evidence suggests greater promise [for medical cannabis] in fibromyalgia than in inflammatory conditions such as rheumatoid arthritis,” said María Julieta Gamba, MD, head of the Rheumatology Department at Hospital Nacional Posadas in El Palomar, Argentina. “But we urgently need well-designed randomized controlled trials with adequate durations and representative samples to clearly establish efficacy and safety.”

“There is still much to learn about the effectiveness of cannabinoids,” added Darío Scublinsky, MD, PhD, associate professor of pharmacology at the University of Buenos Aires Faculty of Medicine, Buenos Aires, Argentina, and editor in chief of the Revista Argentina de Reumatología. “For now, I see two potential uses in rheumatology — fibromyalgia and osteoarthritis — though never as a first-line therapy,” he told Medscape’s Spanish edition.

‘Entourage Effect’

The cannabis plant contains more than 100 cannabinoids, with tetrahydrocannabinol (THC) and cannabidiol (CBD) being the most well known and extensively studied. It also includes flavonoids and terpenes, which give the plant its color and aroma. The so-called “entourage effect” suggests that these compounds work synergistically to produce the plant’s full therapeutic benefit, explained Gamba.

“When we talk about medical cannabis, we tend to focus primarily on CBD oil,” she said. “But to achieve maximum benefit, a small amount of THC — as well as terpenes and flavonoids — is always necessary.”

CBD exerts several biological effects, including reducing anxiety and inflammation, mediated at least in part by its action as a negative allosteric modulator of CB1 and CB2 receptors.

Evidence in Rheumatologic Disease

Jozélio Freire de Carvalho, MD, PhD, rheumatologist and researcher at the Federal University of Bahia’s School of Nutrition in Salvador and adjunct professor at the University of São Paulo Faculty of Medicine in São Paulo, both in Brazil, led a systematic review identifying cannabis therapy as an “interesting option” for several rheumatologic diseases.

Nearly half of the 28 studies analyzed focused on fibromyalgia, and all but one reported significant reductions in pain and improvements in sleep and mood.

In rheumatoid arthritis, two studies showed pain reduction, and one also found decreases in inflammatory markers. Case reports and small studies suggested potential benefits in scleroderma (skin fibrosis and digital ulcers) and dermatomyositis, while three osteoarthritis studies demonstrated notable analgesic effects.

A 2020 meta-analysis found that 1 in 5 rheumatology patients actively use cannabis and experience a significant reduction in pain. Similarly, a survey conducted at an Israeli rheumatology clinic involving 319 patients (82% with fibromyalgia) reported a 77% decrease in pain intensity and a 78% improvement in sleep quality, Gamba noted.

“Osteoarthritis and fibromyalgia are both conditions where our current treatment tools lack strong evidence, where pain control is often inadequate, and where cannabis could represent an alternative,” she said.

Scublinsky noted that cannabis could be considered a second-line treatment for fibromyalgia, especially in patients who cannot tolerate first-line therapies such as duloxetine or pregabalin.

“In osteoarthritis, the picture is more complex because it’s harder to demonstrate efficacy,” he explained. “Current therapies are only modestly effective but help some patients. Still, lifestyle measures — such as weight loss and walking when possible — remain the most beneficial. For patients who have exhausted other treatment options, cannabinoids may be considered.”

There is also emerging evidence of benefits in scleroderma when previous treatments fail — “not for immune control of the disease, but for managing pain and digital ulcers,” he added.

Gustavo Casado, president of the Argentine Society of Rheumatology, Buenos Aires, Argentina, said cannabis “could serve as one more option to relieve pain for many patients.” What remains lacking, he added, is “more evidence on its efficacy for each specific condition.”

‘Adverse Events Are Not Excessively Harmful’

Although cannabis has been used medicinally for millennia, its modern clinical adoption has been limited by concerns about abuse potential and regulatory restrictions. Both speakers, however, placed these concerns in perspective.

They noted that opioids such as tramadol are still commonly prescribed to patients with fibromyalgia with acute pain or older adults with osteoarthritic knee pain and insomnia. In contrast, many countries in Latin America and elsewhere have legalized cannabis for medical or even recreational use, leading to improved product standardization and safety oversight.

“At the doses used medically, cannabinoids are quite safe,” said Scublinsky. “They do not cause excessively harmful adverse effects — these are comparable to those of daily psychotropic medications such as benzodiazepines or opioids. And in terms of dependence, medical-dose cannabinoids are no more addictive than those same drugs.”

De Carvalho, lead author of the most recent comprehensive review on medical cannabis in rheumatologic diseases, noted that in Brazil, the only officially approved formulation for medical use is oral or sublingual, supplied as standardized oil-based solutions that allow for gradual and safe titration. Other routes of administration (such as inhaled or topical forms) appear in studies or are available in some countries but are not yet regulated for clinical use in Brazil.

“In patients with chronic pain, especially fibromyalgia, treatment can begin with CBD-dominant formulations, assessing tolerance and response,” de Carvalho explained. “If necessary, small amounts of THC, typically administered at night, can be added to optimize sleep and analgesia. The key is to establish clear therapeutic goals — for example, a ≥ 30% reduction in pain over 4-8 weeks — and to monitor efficacy and adverse events before continuing treatment.”

Still, both stigma and limited research hinder broader adoption.

“There remains a reluctance to prescribe cannabis, even in countries where it is legally available,” de Carvalho said. “At the same time, we need stronger evidence. Many studies have small samples, short follow-up periods, and wide variability in products and dosing, which limit comparison and guideline development. Even so, the safety profile is generally mild — most adverse effects include drowsiness, dizziness, and dry mouth, with low rates of dependence — and the analgesic benefits in fibromyalgia and osteoarthritis appear clinically significant for some patients.”

“In conclusion,” he said, “medical cannabis is a reasonable and promising adjuvant option, but its use should be accompanied by careful dose titration, clear therapeutic objectives, and ongoing pharmacovigilance, while the medical community continues to produce robust randomized trials and long-term data.”

Gamba and Scublinsky reported receiving honoraria from pharmaceutical companies not involved in medical cannabis production. De Carvalho declared no relevant financial conflicts of interest. 

This story was translated from Medscape’s Spanish edition.