On 29 January, cannabis will be reclassified from a Class B to a Class C drug. On 24 January, the Home Office will launch a £1m campaign through radio, leaflets and posters, to convey the message that "cannabis is still illegal".
One month after this, a new campaign will target 13 to 18-year-olds with health messages, but will only mention mental health in passing.
The charity says that the downgrading from Class B to C will influence young people to believe that cannabis is no longer a serious drug and largely risk-free. Chief executive Cliff Prior said: "Cannabis is not risk-free. We have known for years that using cannabis makes the symptoms of schizophrenia far worse in people who already have the illness. Now there is evidence showing that cannabis can trigger schizophrenia in people already at risk."
Rethink wants to see the Government counter the 'risk-free' message with a long-term, well funded campaign to educate people about the mental health risks.
"Government advertising should concentrate on the real and specific mental health dangers, not general warnings that no-one will take seriously," said Prior.
"January 29 should become an annual Drug Action Day when we all come together to make sure people know the risks they are running with their mental health."
Social care charity Turning Point, which works with people with drug problems, mental illness and learning disabilities, supported Rethink's call for better education about the effects of cannabis but also gave its blessing to reclassification.
The charity's chief executive Victor Adebowale said: "There are 2 million people who use cannabis on an occasional basis. It is far less harmful than many other drugs in terms of health, physical addiction, and links to crime. Reclassification reflects this and allows us to be credible about the information we give out about drug use."
- See Newsmaker, p14.