Times change and cannabis is no exception. The French market is still dominated by conventional products, mostly imported from Morocco – about 200 tonnes a year – but the smugglers are updating their methods.

"The goods are completely different from 10 years ago," says Superintendent François Thierry, head of France's Central Agency for the Repression of Drug Trafficking (OCRTIS). "The world of cannabis is undergoing a complete change."

An all-natural product with a low tetrahydrocannabinol (THC) content is a thing of the past. Thierry says the development of new strains of cannabis has seen concentrations of THC, the psychoactive substance found in cannabis, increase sharply in the space of a few years. According to him these substances bear no relation to what people were smoking in the 1970s.

The new varieties of cannabis are increasingly competing with Moroccan hashish. They are more expensive, but more sought after, due to their higher quality. And the high that is enjoyed by consumers is quite different too.

Things have changed so much the Dutch authorities are considering putting the strongest forms cannabis back on the list of hard drugs. In the streets of Amsterdam, where punters can buy and consume cannabis in the renowned coffee shops, trade in locally produced substances outstrips imported goods.

With more than 5,000 greenhouse plantations, the Netherlands is the main source of this new-generation marijuana, only rivalled by the UK. In both countries, production is increasingly under glass or in cellars. No longer a craft activity, growing is becoming an industrial process, with traffickers moving into the business. A similar pattern is emerging in Germany, Belgium and south-east Europe, in particular Albania.

In February, French police discovered an illegal operation with 700 plants in a warehouse at La Courneuve, north-east of Paris. "If they're growing more than 200 plants at a time, you can be quite sure it's not some sort of family outfit, but definitely organised crime," says Thierry.

Despite being Europe's biggest cannabis consumers, the French lag behind other countries when it comes to large-scale production.

"There is not much being produced here. It's increasing but, with just a few exceptions, it is mainly a case of very small operations. Dealers are still purchasing their supplies abroad. This is certainly helped by the proximity of the Netherlands and southern Spain, where they have established contacts," Thierry adds.

On 5 July, OCRTIS officers arrested a Spaniard who had hidden half a tonne of cannabis resin in a lorry arriving from Morocco.

Dealers are nevertheless adapting to new circumstances. Much as anyone else in trade they are obsessed with costs. The tuned-up go-fast saloons, which featured so largely in films some years back, are now being replaced by less conspicuous means of transport.

There are inevitably risks inherent in transporting illegal drugs over long distances. In particular they may be impounded by the police or customs. So in the best traditions of cops and robbers, traffickers are constantly inventing new methods. One of their latest finds is synthetic-cannabis nasal sprays sold on the internet.

This article originally appeared in Le Monde

• This article was amended on 18 October 2011. The first paragraph of the original article, as translated from the French, referred to "genetically modified" cannabis. The Guardian understands the cultivation of stronger forms of cannabis as described in the article would be the result of methods such as selective breeding. The reference to genetically modified cannabis in the article, as well as in our headline, has therefore been removed. A quote by Superintendent François Thierry in the third paragraph has been replaced with reported speech to convey his main point about an increase in the potency of cannabis — this is to avoid an ambiguity in the original quote that referred also to synthetic cannabis (though rendered by the Guardian as GM cannabis), which contains no THC. The sentence on how the Dutch may consider reclassifying cannabis has been amended to clarify that this relates to the strongest concentrations of cannabis.