A loophole in Japan's drug laws that made selling and eating "magic mushrooms" will soon be stuffed.

The hallucinogenic fungi sprouted through a gap left in the country's law when it was last rewritten in 1990. The legislation banned the drugs psilocybin and psilocin but not the mushrooms that naturally produce them.

Specialty shops and mail-order catalogues soon glommed onto the idea that selling the mushrooms was perfectly legal so long as they weren't labelled as food or drugs.

But the days of buying the shriveled brown mushrooms so bitter they're almost inedible – technically they've been listed as poisonous plants – over the counter are soon to be gone.

The law has been amended. Beginning on June 6, possession of 'shrooms will carry a maximum prison term of seven years, making it an offence on par with cocaine possession.

The crackdown will uproot an industry that has mushroomed in recent years. The owner of a three-store chain said 3,000 people buy mushrooms every month.

The number of people treated for overdoses increased from one in 1997 to 38 in 2000.

Japan's health ministry says there are at least 11 species of magic mushrooms on the market, most of them imported from the Netherlands where they grow on farms.

Mushrooms are not considered addictive, but drug experts say they could lead to other, stronger drugs.

Drug use in Japan has been on the rise since the mid-1990s. In 2001, police seized 40 per cent more illegal narcotics than in the year previous.