Entrepreneurs have high hopes for cannabis in Switzerland, where business has suddenly taken off in recent months, six years after the country legalised low-potency "marijuana-light".

Switzerland changed its laws in 2011 to let adults buy and use cannabis with up to 1 percent THC, the chemical compound that produces a high. But its money-making potential seems only to have been discovered late last year, officials said.

"It started gradually last year, and then suddenly things went crazy in December 2016 and in 2017," said a spokesman for Switzerland's Customs Agency in Berne, which taxes the trade.

The number of retailers registered to sell low-THC cannabis has risen to 140 from just a handful last year, the agency says.

It expects revenue of around $25 million on legal sales of $100 million from cannabis in 2017, although the spokesman said the figure could be far higher if the boom continues.

KannaSwiss, a wholesaler that supplies shops with organically-grown low-THC cannabis to smoke or take orally, has quadrupled its staff to 20 since last year, but boss Corso Serra di Cassano says the company still can't keep up with orders.

The company was founded by two scions of aristocratic families: di Cassano, whose lineage includes an Italian prince beheaded in 1799, and Boris Blatnik, whose sister married into the deposed royal family of Greece. They compare the high from low-potency pot to drinking a couple glasses of wine.

"You feel like you should be high, because you have a body high, but your mind is completely clear," said di Cassano, walking among 3,000 plants inside a brightly lit grow room whose electricity bill runs to $15,000 a month.

Nearby, dried cannabis with a retail value of roughly $1 million sits in six large plastic barrels, ready for delivery.

"We're really seeing the boom in the last month or two," di Cassano said.

MIXED USERS

Switzerland's experimentation with low-THC cannabis comes as several U.S. states have decriminalised or legalised pot.

Europe has a patchwork of laws. The Netherlands is known for coffee shops where the authorities allow sales of small quantities of marijuana. In January, Germany's lower house of parliament passed a law legalising medical cannabis.

Several countries have explored changing the rules to reduce penalties for possession of marijuana or permit strains low in THC. But the Swiss were among the first to make recreational low-potency pot fully legal and tax it.

Paul Monot, a founder of Doctor Green's cannabis shop in Geneva, said his store's trade has grown briskly following its December opening, hitting monthly revenue of 50,000 to 100,000 Swiss francs on sales of four to eight kilos. He now has plans to begin marketing products in up to 40 stores.

"Our customers are very mixed. It is really not only the stereotype of unemployed joint smokers, wearing backward caps and sneakers," Monot said. "They are from all walks of life: 88-year old people are coming, as well as workers, bankers and lawyers."

Carole Rodriguez, a 58-year-old nurse from southern Switzerland, said she visited Doctor Greens to take the edge off her arthritis.

"I am going to brew it in a herbal tea, to fight against pains linked to my joints," Rodriguez said. "I'll try to cook it in small biscuits, but I'd rather eat it than smoke it because I am not a smoker."

The authorities are still adjusting. Police in Zurich and nearby Schaffhausen still confiscate cannabis when their officers find people using it, arguing it is impossible to discern whether its THC content falls within the legal limit without an expensive test. Geneva police said they were also looking for ways to check whether a batch of cannabis is legal.

Barbara Broers, vice-president of the Swiss Society of Addiction Medicine, said there could still be health risks, for example if growers use pest control chemicals.

"We don't know what is in it. There are inadequate checks of really what is in the substance," Broers said.

KannaSwiss's di Cassano said his company welcomes more rules to improve quality.

"The money is great, it's a good thing to do," he said. "But to me, that health aspect, that people are getting a healthy product, is much more important than a quick buck." ($1 = 0.9938 Swiss francs)