Dallas ? If your first antidepressant doesn’t eliminate your symptoms, try, try, again, according to a landmark depression study headed by Dallas researchers.

Two-thirds of people suffering from depression may not fully recover with their first medication. But nearly 30 percent of those patients will experience full remission by either switching to a new medication or adding a second drug to their regimen, according to two articles published today in the New England Journal of Medicine.

The study also indicates that patients starting an antidepressant medication may have to wait more than 12 weeks to see results and shouldn’t stop treatment prematurely.

The results could affect treatment for the nearly 1 in 10 adult Americans who suffer from the condition.

“The bottom line is, if you can hang in there for at least two different treatments, you have a better than 50 percent chance of not just getting better, but getting well,” said John Rush, vice chairman of clinical sciences at the University of Texas Southwestern Medical Center at Dallas and the study’s principal investigator.

“Patients and doctors should not give up treatment after four weeks. And they should expect at least two treatment attempts to become asymptomatic.”

The findings mark phase two of the six-year, $35 million national depression treatment study, one of the most ambitious of its type ever conducted. Sponsored by the National Institute of Mental Health and coordinated by UT Southwestern, it’s the first to gauge how antidepressants work among everyday patients in private practice and public clinics, outside the structure of clinical trials.

Results from phase one of the study, released in January, showed that almost half of nearly 3,000 people suffering from depression recovered or at least improved with use of an antidepressant, in this case, the drug Celexa. One-third experienced a total remission – the virtual absence of symptoms. The patients were monitored at more than 40 primary care and psychiatric clinics across the country.

In phase two, researchers asked those patients who were resistant to the initial treatment and who chose to continue with the study – some 1,400 people – to choose a second, common treatment path. The vast majority either switched drugs or added a second to the Celexa.

Of those who switched drugs, 25 percent experienced a full recovery, as did 30 percent of those who added a drug. But the relief took up to 14 weeks.

“What this says to patients is, it’s important to not give up if the first treatment doesn’t work fully, or causes side effects,” Rush said. “The second step is nearly as effective as the first one. Different people may respond better to one than to another.”

Everyone in the study received some form of treatment; there was no placebo group. The antidepressants, chosen for their frequent use and prescription, were provided by drug companies at no charge. Those patients who switched drugs were randomly assigned to either Wellbutrin, Zoloft or Effexor. Patients who added a drug took either Wellbutrin or Buspar.

In the switch study, there was no significant difference in how the antidepressants performed, despite the fact that they work in different ways. In the augmentation study, Wellbutrin performed slightly better in terms of symptom reduction and side effects than Buspar.