A TV advertisement warning young people of the damage cannabis can do to the brain is to be screened as part of a drugs awareness campaign.
Paranoia is a symptom of too much cannabis
The advert, by drug helpline Frank, is set in a brain shop in the future where customers can buy new brains when their own has become too addled.
It aims to show that prolonged use of cannabis can lead to mood swings, poor motivation, paranoia and vomiting.
But mental health charity Rethink said it did not outline all the risks.
The commercial, to be aired from Monday, features a spooky shop assistant who advises spaced-out customers how best to choose a new brain.
Drug of choice
The so-called Brain Store is stocked with more than 20 different brains, cerebral fluid and memory stalks, all catering for the symptoms of cannabis use.
A spokesman from Frank said they were particularly targeting 11- to 17-year-olds.
He added that although cannabis was being produced to be stronger than ever before, it was clear from its helpline and case studies that the class C drug was growing in popularity.
The advert wants to reach 11- to 18-year-olds
"We know more and more that cannabis is the drug of choice of young people," he said.
"The aim is to drive home that cannabis is harmful."
But Paul Corry, the director of public affairs for Rethink, said the commercial did not go far enough.
"Rethink believes these adverts fall far short of the commitment given by the then Home Secretary Charles Clarke for a 'massive' health education campaign highlighting mental health risks.
"Government must honour its promises so that young people are aware of the true risks of cannabis."
Frank was launched three years ago by the government and gives drugs advice over the phone, online and face to face.
Marjorie Wallace, chief executive of the mental health charity Sane, sad: "We are concerned that advertisements like these alone will increase the growing popularity of cannabis amongst young people. They cannot undo the damage caused by previous confused messages, nor warn sufficiently about the fact that cannabis, particularly Skunk and its other forms, can have far more serious effects than the advertisements appear to suggest. The drug can not only alter the thoughts and feelings of those taking it, but in those who are susceptible it can alter the mind and lead to life-long illness such as schizophrenia.
"Every day there is new evidence of the links between cannabis use and serious mental illness, and a recent study showed that 8 out of 10 of those experiencing first episode psychiatric disorders were heavy users of the drug. Until we know more about the direct effects of cannabis and its derivatives on the developing brain, we should not be relying on awareness messages alone. We need to give clear direction to young people and their families, to teachers and the police, that the drug is illegal and provenly dangerous to a significant number of people."