1. Cancer pain relief with a guide to opioid availability;World Health Organization,1996
2. World Health Organization model list of essential medicines;World Health Organization,2007
3. Cancer pain relief;World Health Organization,1986
4. Narcotic drugs: Estimated world requirements for 2007; statistics for 2005;International Narcotics Control Board,2007
5. Narcotic drugs: Estimated world requirements for 2009; statistics for 2007;International Narcotics Control Board,2009