In fact, during my 15-to-20-minute medication visits with patients, I was often gratified by the effectiveness of the medications I prescribed. For perhaps a quarter of them, medications worked so well as to be nearly miraculous. But over time I realized that the majority of patients need more. One young woman I saw was referred to me by a nurse practitioner for treatment of depression that had not responded to several past antidepressants. She was struggling to raise two young children and was worried that she was doing a poor job of it. Her husband worked full time and was rarely available to help. She cried throughout our initial interview. I started her on Effexor and referred her to a social-worker colleague. She improved initially, but over the years since, her symptoms have waxed and waned. When she reports a worsening of her anxiety or depression, my first instinct is to do one of three things — switch medications, increase her dosage or add another. Over the course of 15 or 20 minutes, this is about all I can offer.

My treatment of this young woman follows the “split treatment” model, but a less charitable description is “fragmented care.” Like the majority of psychiatrists in the United States, I prescribe the medications, and I refer to a professional lower in the mental-health hierarchy, like a social worker or a psychologist, to do the therapy. The unspoken implication is that therapy is menial work — tedious and poorly paid.

But over the past few years, research studies have shown that therapy is just as effective as medications for many conditions, and that medications themselves often work through the power of placebo. In one study, for example, researchers did a meta-analysis of studies submitted by drug companies to the F.D.A. on seven new antidepressants, involving more than 19,000 patients. It turned out that antidepressants are, indeed, effective, because on average patients taking the pills showed a 40 percent drop in depression scores. But placebo was also a powerful antidepressant, causing a 30 percent drop in depression scores. This meant that about three-quarters of the apparent response to antidepressants pills is actually due to the placebo effect.

Nobody knows exactly how the mysterious placebo effect works, but it is clear that it has impacts on the brain that can be seen as clearly as medication effects. In one study conducted by pain researchers at the University of Michigan, subjects were given an ache-inducing injection of saline into their jaws and were placed in a PET scanner. They were then told that they would be given an intravenous pain treatment, but the “treatment” was merely more saline solution, acting as a placebo. The PET scan showed that the endogenous endorphin system in the brains of the subjects was activated. The patients believed so strongly that they were receiving effective treatment that their brains followed suit. Presumably, a corresponding brain change occurs when depressed patients are given placebo pills.

Like placebo, psychotherapy has typically been considered a “nonbiological” treatment, but it has become clear that therapy, like placebo, also leads to measurable changes in the brain. In an experiment conducted at U.C.L.A. several years ago, with subjects suffering from obsessive-compulsive disorder, researchers assigned some patients to treatment with Prozac and others to cognitive behavior therapy. They found that patients improved about equally well with the two treatments. Each patient’s brain was PET-scanned before and after treatment, and patients showed identical changes in their brain circuits regardless of the treatment.

In depression treatment, too, pills and therapy each lead to brain changes, but in this case they appear to be intriguingly distinct. In studies by Helen Mayberg, a professor of psychiatric neurology at Emory University, depressed patients given cognitive behavior therapy showed decreased activity in the frontal lobe, the brain center that might be responsible for the overmagnification of life’s problems that leads to depression in some patients. And they showed increased brain activity in parts of the limbic system, a brain region associated with strong emotion. But Mayberg found that when patients were given medication, their brain activities changed in the opposite direction, stimulating the frontal lobe and damping down the limbic system. “Our imaging results suggest that you can correct the depression network along a variety of pathways,” she said.