The Philippine National Police (PNP) is monitoring the smuggling of a potent black cigarette known as “Thuoc Lao” following reports of teenagers suffering seizures after smoking the product, officials said Wednesday.

Acting PNP Chief Gen. Jose Melencio Nartatez Jr. said intelligence units are working with the Bureau of Customs and the Department of Health to stop the proliferation of the illegal tobacco.

Thuoc Lao, which originates from Vietnam, has a nicotine content of up to 9 percent, far exceeding the 1 to 3 percent found in standard cigarettes. Authorities also suspect some variants are laced with synthetic cannabinoids. The National Tobacco Administration has not authorized its sale or importation.

The warning comes amid a massive crackdown on tobacco smuggling. On Tuesday, police and customs agents intercepted a motorized boat off Manalipa Island in Zamboanga City, seizing 332 master cases of undocumented cigarettes valued at P21.25 million.

Three crew members were arrested after they failed to provide proper cargo documents, according to Brig. Gen. Edwin Quilates, director of Police Regional Office 9.

“This interception in the first week of January clearly demonstrates our commitment to secure our maritime borders and suppress smuggling,” Quilates said.

The PNP is investigating whether the Zamboanga seizure is linked to a string of billion-peso busts over the holidays.

On New Year’s Eve, authorities confiscated P1.1 billion worth of cigarettes in Batangas City, followed by a P1.5-billion seizure in Malabon City on New Year’s Day.