Singer George Michael has been dubbed "stupid" and "naive" by mental health charity Rethink for being filmed smoking cannabis on an ITV programme.
George Michael is currently on his greatest hits tour
Michael is seen lighting what appears to be a cannabis joint on a South Bank Show special in Madrid, and says: "This stuff keeps me sane and happy."
The charity expressed concerns that the drug can be a cause of serious mental health problems.
A spokeswoman for the 43-year-old star declined to comment on the issue.
The ITV show said: "The interview was conducted in Madrid and at his home in England. We must make it clear that when he was smoking he was in Madrid where cannabis is legal."
Paul Corry from Rethink said: "Cannabis is not a risk-free drug. For a significant minority of people it is a trigger for developing a severe long term mental illness like schizophrenia.
"Those most at risk are young people, the core of George Michael's audience, and people who use it over a long period of time and in large amounts," he added.
Drug and alcohol treatment charity Addaction are also worried about the singer's actions.
The group's William Butler said: "We are concerned about the message this can send out to young people, especially when there is such confusion about the legality of cannabis."
Michael, who was being filmed during his greatest hits tour, also said: "It's a great drug, but obviously it's not very healthy. You can't afford to smoke it if you've got anything to do. Anything at all would be foolish."
The former Wham star added that it could be a "terrible, terrible drug" and that it could "chill you out to such a degree that you could lose your ambitions," but denied having a drug problem on camera.
The singer has been found slumped at the wheel of his car twice. He was cautioned by police for possessing cannabis after the most recent incident earlier this month.