Oral administration of ajulemic acid (AjA), a cannabinoid acid devoid of psychoactivity, reduces joint tissue damage in rats with adjuvant arthritis. Because interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNFalpha) are central to the progression of inflammation and joint tissue injury in patients with rheumatoid arthritis, we investigated human monocyte IL-1beta and TNFalpha responses after the addition of AjA to cells in vitro. Peripheral blood and synovial fluid monocytes (PBM and SFM) were isolated from healthy subjects and patients with inflammatory arthritis, respectively, treated with AjA (0-30 microM) in vitro, and then stimulated with lipopolysaccharide. Cells were harvested for mRNA, and supernatants were collected for cytokine assay. Addition of AjA to PBM and SFM in vitro reduced both steady-state levels of IL-1beta mRNA and secretion of IL-1beta in a concentration-dependent manner. Suppression was maximal (50.4%) at 10 microM AjA (P<0.05 vs untreated controls, N=7). AjA did not influence TNFalpha gene expression in or secretion from PBM. Reduction of IL-1beta by AjA may help explain the therapeutic effects of AjA in the animal model of arthritis. Development of nonpsychoactive therapeutically useful synthetic analogs of Cannabis constituents, such as AjA, may help resolve the ongoing debate about the use of marijuana as medicine.