Sadiq Khan has backed calls for the partial decriminalisation of cannabis possession, as a wide-ranging study suggests the way the drug is policed causes greater harm to society than its usage.

In particular, it found, the use of stop-and-search powers disproportionately affects black communities.

“I’ve long been clear that we need fresh thinking on how to reduce the substantial harms associated with drug-related crime in our communities,” the London mayor said on Wednesday.

He added that the report said the “current sentencing for those caught in possession of natural cannabis cannot be justified given its relative harm and people’s experience of the justice system”.

The independent London Drugs Commission, which has produced the report a year after being set up by Khan, stressed it was not promoting the blanket legalisation of cannabis. Rather, its central recommendation was that possession of small quantities of natural cannabis for personal use should no longer be criminalised.

The production and distribution of the drug should still be tackled by police, it said. And it explicitly excluded synthetic cannabis from its decriminalisation calls.

The commissioners, led by the former justice secretary Lord Falconer KC, worked with academics from University College London to gather evidence from more than 200 experts and academics from around the world.

They found that making cannabis a Class B drug under the Misuse of Drugs Act is “disproportionate to the harms it can pose relative to other drugs controlled by the act”.

The researchers said: “The sentencing options currently available, especially for personal possession, cannot be justified when balanced against the longer-term impacts of experience of the justice system, including stop and search, or of serving a criminal sentence can have on a person.”

They added that policing of the drug focuses on certain ethnic communities – particularly the black community – “creating damaging, long-lasting consequences for individuals, wider society, and police-community relations”.

While they found potential short-term benefits in legalisation, such as tax revenues and reductions in criminalisation, they stressed that the “extent of harms, particularly with respect to public health, as well as personal and societal costs, take longer to emerge and are not yet well understood”.

The researchers said greater focus needed to be placed on helping the minority whose use becomes problematic, noting that cannabis can be addictive. “Those who suffer from the adverse effects of cannabis, which may be a small percentage of users but is a high number of people, need reliable, consistent medical and other support.”

Further, they said education about cannabis was inadequate, failing to “acknowledge drivers of use” and – particularly where younger people are concerned – being “led by providers who lack sufficient credibility and insight”.

Falconer said: “It is clear that a fundamental reset is required. Legalisation is not the answer. The criminal justice system response needs to focus only on the dealers and not the users … And there needs to be much more education on the risks of cannabis use.”

Khan said the report made recommendations to which authorities in both City Hall and Westminster needed to pay attention.

A Home Office spokesperson said: “We will continue to work with partners across health, policing and wider public services to drive down drug use, ensure more people receive timely treatment and support and make our streets and communities safer. We have no intention of reclassifying cannabis from a Class B substance under the Misuse of Drugs Act.”