 Ethnic militias and rebel groups (in particular the United Wa State Army) are responsible for much of this production; however, the Burmese military units are believed to be heavily involved in the trafficking of the drugs.Burma is also the 2nd largest supplier of opium (following Afghanistan) in the world, with 95% of opium grown in Shan State.Illegal narcotics have generated $1 to US$2 billion in exports annually, with estimates of 40% of the country's foreign exchange coming from drugs.