Those were the words last week of Harrogate mum Suzanne Knowles, mother of Jake Knowles, a student who hanged himself from a banister at his university lodgings after a prolonged struggle with cocaine. Suzanne Knowles says her son's personality was altered by the drug and the coroner agreed that long-term cocaine abuse had affected Jake's health.

Jake was 21 when he died. An intelligent and outgoing politics and philosophy student at Manchester Metropolitan University, he had begun using cocaine two years before his death. But he had started smoking cannabis when he was 14.

I am a Harrogate mum, too. While having lunch recently with a few of my Harrogate mum friends, the daughter of one, a Year 7 pupil, remarked that "half the Year 8s were smoking weed". We rolled our eyes and let it pass, but later, I asked my own daughter, then a Year 8 – age 13 – if it was true.

"Well, maybe not half, but yeah, loads are," she said. Where? "Oh, you know, in town, in the park ..." What, in the lovely Valley Gardens? "Er, yeah, I think so ..."

Anyone who doubts that smoking cannabis can progress easily to a cocaine habit should think about Jake Knowles. Let's not forget that strong links have been found between cannabis itself and depression, particularly associated with teenage smoking of the drug.

Of Jake's cocaine use, recording a verdict of suicide, Manchester coroner Nigel Meadows said he was "convinced that this drug has been the root cause of his death". Jake's mother, who is a doctor of philosophy, is convinced of it too, and is calling for more to be done to teach youngsters about the consequences of drug-taking.

Drug use, she said, was a taboo subject. She spoke of an undercurrent of drug-taking among Harrogate teenagers: "Harrogate is known as one of the worst drinking spots for red wine in the country. This is the same, but their kids are doing cocaine on a Saturday night instead."

I know parents who point-blank refuse to believe in the idea that their teenager might use drugs. I also know parents who smoke cannabis and don't mind their children doing so. Both are examples of misguided, outdated, stupid and dangerous parenting, but the most dangerous parents are the ones who won't accept that drug-taking is a real problem for all children – including their own.

For three decades at least, middle-class parents have refused to acknowledge teenage drug use. The current generation of parents ought to know better. Those who don't should learn fast. So step out of your gleaming pearl-granite top kitchens. Wake up and smell the cannabis.