BEIJING - Chinese law enforcement authorities are grappling with a new enemy in the war on drugs -- synthetic drugs such as methamphetamine, according to the State Food and Drug Administration.

In a survey among 203,000 drug addicts from drug rehabilitation and detention centers, the administration found 50.7 percent of drug users are under 35 years old. The ratio is even higher for synthetic drug addicts -- 70.1 percent of them are under 35.

The share of heroin among registered addicts continued to drop, though it still accounts for a majority of drug use at 66.8 percent in 2013. Meanwhile, the use of synthetic drugs has climbed to 33.9 percent.

The survey found that more than 80.5 percent of new addictions are to synthetic drugs, some 80 percent of which are methamphetamine.

New methods of drug trafficking are posing new challenges to the authorities. Li Jun, deputy director of a county-level public security bureau in southwest China's Yunnan Province, which boarders Myanmar and Laos, told Xinhua in June that many synthetic drugs are smuggled disguised as coffee, candy, juice and tea and it is more difficult to uncover such drug cases.