A mental health charity has called for a government inquiry into the effects that cannabis has on users.
Cannabis use can affect people predisposed to mental illness
Rethink wants the Commons Health Select Committee to launch an investigation "to help establish the facts about the link between cannabis and psychosis".
It comes a year after cannabis was reclassified from a Class B to a Class C drug - a move the charity claims sent a "confusing message" to young people.
A Department of Health spokesman said they were commissioning a review.
"We have no objection to the health select committee looking into this," he said.
"However we are in the process of commissioning an expert review of all the academic and clinical evidence of the link between cannabis use and mental health, particularly schizophrenia.
"There is medical clinical evidence now that there is an important causal factor between cannabis use and schizophrenia - not the only factor, but an important causal factor. That is the common consensus among the medical fraternity."
Cannabis was reclassified so that police could target hard drugs.
Rethink said there had been a 60% increase in people who smoked drugs and had mental health problems in the last five years.
Most medical experts agree that smoking cannabis in itself does not cause mental illness, but that people who are predisposed to psychosis are much more likely to develop symptoms if they use the drug regularly.
"Cannabis is not risk free," Rethink chief executive Cliff Prior said.
"We have known for years that using cannabis makes the symptoms of schizophrenia far worse in people who already have the illness."
Calling for further research, Mr Prior said the government should "concentrate on the real and specific mental health dangers, not general warnings that no-one takes seriously".
Home Office figures released on Friday showed that arrests for possession of cannabis fell by a third in the first year of its reclassification.
Based on the feedback from the 26 police forces, there were an estimated 43,750 arrests in the last 12 months compared with 68,625 in the previous year.
In response to the figures, drug education charity DrugScope called for more debate on drug education and prevention, particularly in schools.
"We need to move on from the debate on cannabis reclassification to concentrating on practical responses to drug use and harm," said chief executive Martin Barnes.
Campaigner Terry Hammond says his son, Steve, developed schizophrenia after taking cannabis resin.
"I have got absolutely no doubt at all, and neither has Steve - Steve is absolutely clear about it - that it was the cannabis that triggered it.
"It may not have been the absolute cause of it, but it was the trigger.
"It is Russian roulette," he said. "For some people it can ease pain, but for others it can be an absolute disaster."
But Steve Barker, of the Campaign to Legalise Cannabis Association, said that by prohibiting cannabis it was preventing information about its use being readily available, while cannabis could in fact aid those with medical problems.
"There is a larger proportion of people with mental health problems who claim cannabis reduces their symptoms than those for whom it is a problem," he said.
"To criminalise people and to put them though the criminal justice system rather than give them the medical support they need is completely wrong."