This randomized, double-blind, placebo-controlled, and comparator-controlled trial evaluated the safety and efficacy of an enzyme combination, as Wobenzym, in adults with moderate-to-severe osteoarthritis (OA) of the knee. Adults (n=150) received Wobenzym, diclofenac (a nonsteroidal anti-inflammatory drug, NSAID), or placebo for 12 weeks. Improvement in pain scores (Lequesne Functional Index) did not differ between subjects treated with Wobenzym or diclofenac, and both treatment groups improved compared to placebo (P<0.05). Reduction in total WOMAC scores (secondary outcome measure) did not differ between Wobenzym and diclofenac, although only diclofenac emerged as different from placebo (P<0.05). The median number of rescue medication (paracetamol) tablets consumed was less in the Wobenzym group compared to placebo (P<0.05), while there was no difference between diclofenac and placebo. Adverse events were similar in frequency in Wobenzym and placebo groups (7.2% and 9.1% of subjects, resp.) and higher in diclofenac group (15.6%). Wobenzym is comparable to the NSAID diclofenac in relieving pain and increasing function in adults with moderate-to-severe painful knee OA and reduces reliance on analgesic medication. Wobenzym is associated with fewer adverse events and, therefore, may be appropriate for long-term use.