The earliest reported use of drugs among US troops in Vietnam was recorded in 1963. During this time the most commonly used drug was marijuana, which was sometimes used in the form of hashish. Soldiers mainly used the drug during downtime in rear areas and commanders expressed concern that it would hinder combat operations. On the topic, Major General Raymond G. Davis noted that the troops policed themselves while they were out in the field, where combat was possible, as they would need a clear head to survive. Heroin usage was also common among US troops and per historians, was a much larger problem. Opium and marijuana were widely available and sold for low prices by villagers and locals. Vietnamese heroin was more potent and was smoked instead of injected.