The ban on legal highs will not lead to the disappearance of spice and other synthetic, cannabis-like drugs because they are so profitable to dealers, a senior government drugs adviser has warned.

Prof Harry Sumnall, a member of the Home Office’s advisory council on the misuse of drugs (ACMD), said the economics of producing the substances – often collectively dubbed “spice” – versus that of growing traditional cannabis made them an appealing proposition.

Sumnall said the ingredients were easily available online. “We were making some in the lab the other day. Very, very easy to do, pretty much shake and bake. Really easy to make, highly profitable, these drugs aren’t going anywhere.”

Media reports on the harm caused by new designer drugs have focused on spice and similar substances that affect the endocannabinoid system, including reports of users self-harming, exhibiting bizarre behaviours in public and being hospitalised after seizures.

However, Sumnall, who is professor of substance use at the Centre for Public Health, said: “I think, maybe rightly so, that synthetic cannabinoid receptor agonists (SCRAs) get a really bad press, not only from the popular media – and we’ve all seen newspaper headlines and videos of people stumbling around town centres – but perhaps also from researchers as well.

“We have to remember this is a really diverse group of compounds and people use these substances in quite a pleasurable way, they enjoy these substances. Not everyone using these substances are reporting some of these adverse effects, and often we forget that.”

Sumnall was speaking on Tuesday at a closed conference on cannabis treatment hosted by the University of York, where researchers, policymakers and drug workers were trying to make sense of a recent surge in the numbers of people seeking help for cannabis use.

While the dangers of spice and other “novel psychoactive substances” are at the forefront of public consciousness, the numbers of people seeking treatment for their use are minuscule compared with those presenting with problems from using traditional cannabis.

The number of under-18s in treatment for cannabis rose from 9,000 in 2006 to 13,400 in 2015. The drug accounts for three-quarters of the young people receiving help in specialist centres.

Mark Monaghan, of Loughborough University, who had surveyed drug workers on their response to people complaining about cannabis use, said there was no established best practice on how to go about treatment. Many respondents regarded cannabis use as more or less benign compared with the heroin and crack cocaine habits that other service users presented with.

He quoted one drug worker as saying: “I know people who would be absolutely delighted if some of their clients stopped using heroin, stopped using crack cocaine and started presenting to treatment services with cannabis. Some would deem that a success.”