Three charities have teamed up to tackle what they call “the social justice issue of the 21st century” - mental illness. About time too.

Some might sneer at the multimillion-pound Time to Change campaign for using celebrities - such as Stephen Fry, who was diagnosed with bipolar disorder at 37, but in my view anything, up to and including the use of Alastair Campbell in advertising material (“I said to Tony Blair, you do know about my breakdown, don't you?”), is welcome if it encourages more open discussion of mental ill health.

However, as someone with a parent and sibling who suffer from schizophrenia, the most severe of all psychiatric illnesses, I am concerned about the campaign. In its glitzy efforts to show that mental illness need be no bar to becoming rich and famous, and in its enthusiasm to tackle some of the myths surrounding the subject, it glosses over the harrowing effects of more serious psychiatric conditions and creates a myth of its own - that all mental illness is the same.

At the heart of this problem lies the claim that “mental health problems affect one in four people”, a statistic that encompasses conditions ranging from anxiety to depression and schizophrenia. Each of these conditions can, of course, destroy lives. But what do anxiety or mild depression have in common with schizophrenia? Not much, I would argue. Three of the six generalisations in Time to Change's “myth-busting” Tube adverts don't apply to schizophrenia.

The campaign, for instance, claims it is a “fact” that “people with mental illness can and do recover”, which may be true of types of depression but isn't necessarily the case with severe mental illnesses. What happens to people with schizophrenia varies greatly according to sex, age at its onset, the speed of onset, awareness of the illness and initial response to medication. But basically it is a lifelong condition with no cure. Only a tiny number of people have a single episode and then live their lives without medication.

The campaign also claims as a myth that “people with mental illness are violent and unpredictable” and that “people with mental illness are more likely to be a victim of violence”. Again, this is true for depression, but one of the many tragedies of schizophrenia is that sufferers are as much a risk to themselves as to others: between 10 and 15 per cent of sufferers take their own lives.

As E. Fuller Torrey, a leading US psychiatrist, has explained in The Wall Street Journal: “To be precise, mentally ill individuals who are taking medication to control the symptoms of their illness are not more dangerous. But on any given day, approximately half of severely mentally ill individuals are not taking medication. The evidence is clear that a portion of these individuals are significantly more dangerous.”

Then there is the assertion that people are wrong if they think they don't “know anyone with a mental illness” and that “someone you know or love has experienced mental illness”. In this case, my objection is not that the generalisation doesn't apply to schizophrenia, which affects 1 in 100 people, but that the silence surrounding the disease is much more profound and intense.

In my reading on the subject, I have been struck by how commonly friends and family members abandon sufferers because the symptoms - which can include hearing voices, feeling that your thoughts are being broadcast to the outside world, feeling that things are crawling beneath the skin, and believing an alien force is directing you - are so terrifying that people don't know what to do and end up running away. Indeed, it was not until my mid-twenties that I confronted the reality of my father's and sister's schizophrenia.

Schizophrenia really is the modern equivalent of leprosy. I have counselled friends through depression and, as shattering as the effects have been on them, they do not compare to what schizophrenia has done to my family. My father is a gentle and kind man and has been stable for a long time. But he had to live through decades of violent breakdowns, suicidal episodes, a period of imprisonment, endless firings from jobs due to erratic behaviour, and unexplained domestic violence before he got there. And this is what accounts of family lives blighted by schizophrenia are like: the painful narrative keeps lurching forward bleakly until the medication starts working or someone - usually the sufferer - dies.

Pain isn't relative, of course, but, frankly, even Stephen Fry's difficult experience of manic depression doesn't compare. He at least has had the choice of not taking medication, whereas sufferers of schizophrenia don't, and his symptoms have been such that he has managed to garner the nation's sympathy, whereas I can't recall the last time anyone stood up to defend someone with schizophrenia in public, if, as a result of involuntary symptoms, they committed an act of violence.

The Time To Change campaign is doing something noble in pointing out that mental illness needn't be a bar to personal achievement. But in its implication that all mental illness can be overcome, it trivialises more severe diseases and diminishes the harrowing experiences of sufferers.

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