The present invention relates to the use of a combination of tetrahydrocannabinol (THC) and cannabidiol (CBD) in the treatment of multiple myeloma. The combination of THC and CBD appears to be particularly effective in reducing cell viability and cell migration in this disease. Preferably the THC and CBD are used is in the form of a highly purified extract of cannabis such that the cannabinoids are present at greater than 98% of the total extract (w/w) and the other components of the extract are characterised. Alternatively, the THC and CBD may be a synthetically produced cannabinoid.