The benefits and harms of adding ketamine to a strong analgesics pain-killers such as morphine for the relief of cancer pain are not yet established. Only two small randomised controlled trials suggest that when ketamine is given with morphine it may help to control cancer pain. However, these data are insufficient to assess the effectiveness of ketamine in this setting. So far there is little clinical evidence to support this practice, furthermore, the The Cochrane Database of Systematic Reviews 2009 concludes that: "Current evidence is insufficient to assess the benefits and harms of ketamine as an adjuvant to opioids for the relief of cancer pain. More randomized randomised controlled trials are needed".