Many people with developmental disabilities who rely on Medicaid require mental health care, but new research finds that even among clinicians who accept Medicaid, getting an appointment is tough.

Less than 1 in 5 clinicians listed as accepting new patients enrolled in Medicaid were reachable and willing to schedule an appointment, according to a “secret shopper” study published recently in the journal JAMA.

Researchers called randomly selected psychiatrists, nurse practitioners and physician assistants working in the psychiatric field who were listed in provider directories for Medicaid managed care plans in New York City, Los Angeles, Chicago and Phoenix. They asked for the earliest available appointment for an individual with depression. If the clinician they inquired about was unavailable, they asked about other providers.

Appointments were only offered in 18% of cases, the study found. Even when an appointment was available, however, the wait time could be as long as six months.

“We’ve long known that relatively few psychiatrists participate in the Medicaid program, which compromises access to necessary care,” said Dr. William Schpero, an assistant professor of population health sciences at Weill Cornell Medical College who worked on the study. “This is compounded by the issue identified in our study: even among psychiatrists listed as participating in Medicaid, actual access to care is apparently quite low.”

The availability of psychiatric care varied across the cities in the study, researchers noted. Appointments were easiest to come by in New York, with 36% of offices offering a slot with a median wait time of 28 days. By contrast, in Los Angeles, only 15% of clinicians were available and the median wait time was 64 days.

Among the 263 clinicians who were unavailable, 15% had inaccurate or nonworking phone numbers and 35% did not answer on two different tries.

The findings highlight the need for greater enforcement, the researchers said.

“Most states have outsourced the provision of the Medicaid benefit to private health plans,” said Dr. Diksha Brahmbhatt, the study’s lead author who’s now at Brigham and Women’s Hospital in Boston. “It is up to states — with guidance and oversight from the federal government — to ensure these plans construct networks of mental health professionals who don’t just participate in Medicaid on paper, but meaningfully make appointments available to enrollees.”