Outlandish claim about chemical deficiency in depression

Juliette Jowit makes a case in a Guardian comment that parity of esteem in mental health services is a scientific necessity rather than a gracious concession. She rightly indicates that Freud may well have thought that psychoanalysis would be replaced by psychopharmacology. However, she's been badly misled by Tim Cantopher in his book Depressive illness. The curse of the strong. She correctly quotes from Cantopher:-

If I were to perform a lumbar puncture on my patients (which, new patients of mine will be pleased to hear, I don't) I would be able to demonstrate in the chemical analysis of the cerebrospinal-spinal fluid (the fluid around the brain and spine) a deficiency of two chemicals.

Piffle! Cantopher doesn't just not do a lumbar puncture on his patients because it's an unpleasant investigation. It wouldn't show what he suggests. He might be 'struck off' by the GMC for doing an inappropriate investigation. Jowit rightly surmises that Cantopher means serotonin and noradrenaline as the 'two chemicals'. I presume Cantopher believes what he wrote but there are no references in the book, so it's difficult to know where he got the idea from. How does he get away with misleading journalists, let alone patients?

Just to be clear, I'm not advocating mental health problems being dealt with separately in the NHS. Jowit does note that "some psychiatrists have been driven to an obsession with biology". Perhaps she needs to investigate further why the public is being misled about mental illness being a physical illness. As I keep reiterating, do not misunderstand me. Of course mental illness is due to the brain - that's mere tautology. But, to make the claim that Cantopher makes in the quote above is outlandish.