Assess the importance of the mid-term placebo effect of symptomatic slow acting drugs given for osteoarthritis.
We analyzed six controlled trials available in the literature. Trial duration ranged from 2 to 6 months. The trials had been conducted to assess the symptomatic effect of diacerhein, avocado/soya unsaponifiable chondrontin sulfate and oxaceprolin given for osteoarthritis of the hip or knee. The main clinical outcomes assessed were functional impairment using the Lequesnes index and a visual analog scale.
Globally, the trials showed decreased function impairment with a 2 to 3 points decrease in the Lequesnes index (15 to 20%) and a 10 to 16 mm fall in the visual analog scale (-20 to -30%) in the placebo groups.
Our findings confirms the importance of the mid-term placebo effect in the clinical course of osteoarthritis in patients given slow-acting drugs. This placebo effect, observed under these circumstances, is an expression of what clinicians will look for in future drugs and should be helpful for calculating the number of patients required in future trials.