More Americans with psychiatric conditions are being treated with drugs alone compared with a decade ago, while talk therapy -- either by itself or in combination with medication -- is on the decline, a new study finds.

The implications of the trend, as well as its underlying causes, are not fully clear, according to researchers. But they say the findings indicate that outpatient mental health care in the U.S. is being redefined.

The results, reported in the American Journal of Psychiatry, are based on data from two government health surveys conducted in 1998 and 2007.

Over that period, the percentage of Americans who said they'd had at least one psychotherapy session in the past year remained steady -- at just over 3 percent in both 1998 and 2007.

However, among Americans receiving any outpatient mental health care, the proportion being treated with drugs alone rose from 44 percent in 1998 to 57 percent in 2007.

Meanwhile, combined treatment with drugs and psychotherapy declined from 40 percent to 32 percent, and the use of psychotherapy alone slipped from 16 percent in 1998 to about 10 percent in 2007.

National spending on psychotherapy also declined -- from an estimated total of $11 billion in 1998 to $7 billion in 2007. Overall spending on mental health care remained fairly steady, however -- at $15.4 billion in 1998 and $16 billion in 2007- suggesting an increase in the proportion of mental health spending devoted to drug therapies.

This represents a fairly dramatic shift in mental health treatment, and it is not necessarily good news for many patients, said Dr. Daniel Carlat, an associate clinical professor of psychiatry at Tufts University School of Medicine who was not involved in the study.

What concerns me most, he told Reuters Health in an email, is that there was a 20 percent drop in treatment combining therapy with medication.

Such integrative treatment, Carlat said, is often the most effective.

I think there are some reasons for concern, agreed Dr. Mark Olfson, a professor of clinical psychiatry at Columbia University in New York and one of the study's authors.

He said that with depression, for example, there is evidence that combination therapy is superior to medication alone.

In an interview, Olfson pointed out that the largest investigation so far of depression in teenagers found that combined therapy was generally more effective than either drugs or talk therapy alone. In that study, known as TADS (Treatment for Adolescents with Depression Study), combination therapy was better at reducing teens' suicidal thoughts, for example.

Yet the current study of trends in psychotherapy use found that among Americans treated for depression, the proportion on medication alone rose from 41 percent in 1998 to 51 percent in 2007. The percentage receiving combination treatment dipped from 50 percent to 42 percent.

On the positive side, Olfson said, the trend toward greater medication use means that some people who might not have received any mental health care at all in the past are now getting treatment.

Mental health care, he said, is evolving in a way that means more people are receiving treatment, but are not necessarily getting the most effective therapy.

The study was not designed to weed out the reasons for these trends. But one potential factor, Olfson said, is the increased marketing of psychiatric drugs not only to doctors, but to the public as well.

Other factors, he speculated, could include patients' increased acceptance that mental health disorders have biological underpinnings and, for some people, a perception that medication may be the simpler approach -- requiring less time and effort and potentially offering quicker results.

In addition, primary care doctors can prescribe psychiatric medications, while psychotherapy requires a referral to a mental health specialist -- a psychiatrist, psychologist, social worker or mental health counselor.

Primary care doctors now account for the large majority of psychiatric-drug prescriptions issued in the U.S., Olfson and colleague Dr. Steven C. Marcus note in their report.

What all of this means for Americans' mental health is not entirely clear. But Olfson recommended that people who are being newly prescribed a psychiatric medication ask their doctors if any alternative treatments are available for their particular condition.

This is especially relevant for people with milder symptoms. In general, Olfson said, psychiatric drugs have been shown to be most effective for patients with more severe disorders.

Someone with relatively mild depression symptoms, for example, might respond to some form of mental health counseling alone.

The National Institute of Mental Health estimates that one in 10 American adults experiences depression in any given year, and that 18 percent of adults suffer from some form of anxiety disorder.

One of the most common and best-studied forms of psychotherapy is cognitive-behavioral therapy, which involves examining how thoughts affect emotions and learning ways to change behavior patterns that may be negatively affecting a person's mental well-being.