Doctors should quiz younger patients about cannabis use, senior GPs say.
GPs have tended to shy away from addressing cannabis use
The rising availability of strong cannabis was putting teenagers at risk, Dr Clare Gerada, head of the Royal College of GP's drug misuse unit, said.
Cannabis was "more popular among young people than cigarettes and higher potencies more widely available than ever before" she warned.
It is thought that two in five 15-year-olds in the UK have tried cannabis - the highest rate in Europe.
GPs were told at a conference being held in London on Tuesday that they should look to reduce the harm caused by cannabis.
Dr Gerada said that high-strength cannabis was becoming "the norm rather than the exception".
She said: "There is evidence that high levels of use, especially among teenagers who are physically and mentally still developing, carries with it the increased risk of psychosis and respiratory conditions such as asthma.
GPs have traditionally shied away from questioning patients about drugs because of a lack of knowledge of the issue and concerns about patient confidentiality.
But Dr Gerada said they should be talking to their patients about cannabis in the same way they do about smoking and drinking.
The potential harm from using cannabis has been the topic of much research over recent years.
Several studies have linked it to mental health problems, such as depression and schizophrenia, and respiratory illness.
A spokeswoman for the charity Drugscope welcomed the move by family doctors.
She said: "GPs are often the first point of call when people have problems, they are trusted and well-respected so they are the right people to address these issues."
But Drugscope said it was important to recognise that using cannabis did not necessarily cause the health problems but just made them more likely if a user had a history of problems.
Cliff Prior, chief executive of mental health Rethink, also said GPs should be asking young people about their drug habits.
"Young people are hearing that, as a result of the reclassification that took place a year ago, cannabis is no longer regarded as a serious drug and that the police won't make arrests except in the most serious circumstances.
"Young people are getting the message that cannabis is risk-free which is reflected in the astonishingly high rates of use amongst young people as the street drug of choice. "
But GPs told the conference they had been left confused over where they stood on cannabis.
Dr Shahid Dadabhoy, a GP from Chingford, said: "The government has lowered the classification of the drug, but tell us it is still illegal.
"And on the other hand, experts highlight the dangers of over use but also stress potential benefits."