Chemical Imbalances and Mental Illness? Go for the Placebo with Side Effects

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Marcia Angell has a wonderful review, The Epidemic of Mental Illness: Why?, up at the New York Review of Books. I want to highlight two things: (1) the fall of the “chemical imbalances” theory of the brain, cloaked in the language of neurotransmitters and synapses; and (2) that healing matters, in particular signs people can interpret that drugs they are getting must be making a difference.

Chemical imbalances is our most recent folk theory of mental illness in the Western world. A focus on doctors and therapists doing, rather than on how healing happens, is the corollary – the imbalance, whether chemical or psychoanalytic, needs to be corrected. Both of these are rich arenas for medical anthropology, and I particularly hope people will dig into work on how healing and placebos work.

But for those also interested in the brain, Angell’s piece gives some great overview of how our understanding of brain function and treatment is progressing. Here she is on the chemical imbalance approach:

Because certain antidepressants increase levels of the neurotransmitter serotonin in the brain, it was postulated that depression is caused by too little serotonin. (These antidepressants, like Prozac or Celexa, are called selective serotonin reuptake inhibitors (SSRIs) because they prevent the reabsorption of serotonin by the neurons that release it, so that more remains in the synapses to activate other neurons.) Thus, instead of developing a drug to treat an abnormality, an abnormality was postulated to fit a drug.

That was a great leap in logic, as all three authors point out. It was entirely possible that drugs that affected neurotransmitter levels could relieve symptoms even if neurotransmitters had nothing to do with the illness in the first place (and even possible that they relieved symptoms through some other mode of action entirely). As Carlat puts it, “By this same logic one could argue that the cause of all pain conditions is a deficiency of opiates, since narcotic pain medications activate opiate receptors in the brain.” Or similarly, one could argue that fevers are caused by too little aspirin.

But the main problem with the theory is that after decades of trying to prove it, researchers have still come up empty-handed. All three authors document the failure of scientists to find good evidence in its favor. Neurotransmitter function seems to be normal in people with mental illness before treatment. In Whitaker’s words:

Prior to treatment, patients diagnosed with schizophrenia, depression, and other psychiatric disorders do not suffer from any known “chemical imbalance.” However, once a person is put on a psychiatric medication, which, in one manner or another, throws a wrench into the usual mechanics of a neuronal pathway, his or her brain begins to function…abnormally.

Carlat refers to the chemical imbalance theory as a “myth” (which he calls “convenient” because it destigmatizes mental illness), and Kirsch, whose book focuses on depression, sums up this way: “It now seems beyond question that the traditional account of depression as a chemical imbalance in the brain is simply wrong.”

And here is the relevant piece on anti-depressants, placebos, and really getting at the science of what is going on.

Kirsch was also struck by another unexpected finding. In his earlier study and in work by others, he observed that even treatments that were not considered to be antidepressants—such as synthetic thyroid hormone, opiates, sedatives, stimulants, and some herbal remedies—were as effective as antidepressants in alleviating the symptoms of depression. Kirsch writes, “When administered as antidepressants, drugs that increase, decrease or have no effect on serotonin all relieve depression to about the same degree.” What all these “effective” drugs had in common was that they produced side effects, which participating patients had been told they might experience.

It is important that clinical trials, particularly those dealing with subjective conditions like depression, remain double-blind, with neither patients nor doctors knowing whether or not they are getting a placebo. That prevents both patients and doctors from imagining improvements that are not there, something that is more likely if they believe the agent being administered is an active drug instead of a placebo. Faced with his findings that nearly any pill with side effects was slightly more effective in treating depression than an inert placebo, Kirsch speculated that the presence of side effects in individuals receiving drugs enabled them to guess correctly that they were getting active treatment—and this was borne out by interviews with patients and doctors—which made them more likely to report improvement. He suggests that the reason antidepressants appear to work better in relieving severe depression than in less severe cases is that patients with severe symptoms are likely to be on higher doses and therefore experience more side effects.

To further investigate whether side effects bias responses, Kirsch looked at some trials that employed “active” placebos instead of inert ones. An active placebo is one that itself produces side effects, such as atropine—a drug that selectively blocks the action of certain types of nerve fibers. Although not an antidepressant, atropine causes, among other things, a noticeably dry mouth. In trials using atropine as the placebo, there was no difference between the antidepressant and the active placebo. Everyone had side effects of one type or another, and everyone reported the same level of improvement.

Link to Marcia Angell’s The Epidemic of Mental Illness: Why?

The photo was taken by Chris Szbala; the original can be found here. Big hat-tip to Medical Skeptic for pointing it out as “The science of depression: chemical imbalance- the quick and easy version.”

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