That's not what he asked. The question is "can it be measured?" and it can: http://www.clinchem.org/cgi/content/full/44/1/155 and http://www.springerlink.com/content/tq58032421q41q14/ and http://www3.interscience.wiley.com/journal/110436914/abstrac...

I write code for medical devices for a living; if a substance found in the body is therapeutically interesting, then someone, somewhere has built an instrument to measure it :-)

The comment author almost certainly assumed that the measurement would have a meaning - specifically, that it would determine whether he might benefit from a drug.

There is no doubt that we can measure the concentration of dopamine or serotonin in an aqueous solution (and eventually, within a brain.) Whether there can be any clinical point to such a measurement is debatable.

A "Research Center Against Psychiatry" is hardly a reliable source for such a claim.

Read the actual arguments in the linked article, and refute them. The source is irrelevant.

Alternatively, ask an honest psychiatrist whether anyone has any solid idea just why the drugs work, when they work. Or why they don't, when they don't.

"How are the chemical imbalances which are the supposed basis for the prescription of "antidepressants" diagnosed? Is exploratory neurosurgery performed, using some technique that allows the surgeon to quantify synaptic transmitter levels? No, the very idea is absurd. Is a spinal tap, then, done to at least measure, on a gross scale, the distribution of neurotransmitter metabolites? Of course not – how many people have undergone spinal taps before receiving a prescription for Effexor®? Is blood at least drawn, to test something? No. This diagnosis – the diagnosis of the most subtle of chemical disorders in the most complex organ in the body – is made on the basis of the patient's report of feeling sad and lethargic. Try to imagine a hematologist diagnosing leukemia this way to get a sense of just how ridiculous this idea is."

"The principal reason for rejecting biopsychiatry (aside from the fact that intellectual honesty demands its rejection) is that it locates the cause of psychic suffering in people's "bad brains," and excludes the conditions of modern life, or anything else, from consideration as the cause of such pain."

Note also that the author defends your right to take any drug, if you wish to. However, he defends it from the personal freedom point of view, and attacks the (popular yet unfounded) notion that these drugs return the individual to some nebulous ideal of "mental health."