Until the middle of last year, the quasi-legal synthetic drug “dappo habu” (“loophole herb”) was readily available in Tokyo’s nightlife scene. 

The drug is called “loophole herb” because it is similar to synthetic marijuana “Spice” or “K2” as it is known in the West. When a certain strain is banned, producers of dappo herb would tweak the formula, playing a legal cat-and-mouse game as the new variant would slip under the legal radar again for a time, reports MarketWatch.

The authorities’ attempts to ban synthetic marijuana in the U.S. has dealt with a similar challenge. Despite laws prohibiting manufacture, sale or possession of synthetic marijuana, more powerful and technically legal strains are developed to outrun these laws.

In Japan, the authorities were reportedly more effective at curbing dappo herb. Last July, the country’s Ministry of Health, Labor and Welfare launched a public awareness campaign that effectively rebranded dappo herb as “kiken” (“dangerous”) drug. A wave of police busts and some incidents — including a motorist driving onto a sidewalk, killing one pedestrian and injuring seven—in the national press drove the message home.

“The police cracked down on it heavily in recent months,” a head shop clerk in Shibuya told MarketWatch. “It used to be easy to find, but you can’t buy it legally anymore.”