For example, in some countries, direct referrals from the criminal justice system account for a high proportion of treatment admissions. The abuse of heroin and synthetic opioids remains relatively low in the European Union. The average annual prevalence of opioid use, mainly of heroin, among the general population between 15 and 64 years of age was estimated at about 0.4 per cent. In 2013, opioids were the primary drug of abuse for 41 per cent of all those receiving drug abuse treatment in Western and Central Europe.