Whether it's an undiagnosed disorder or no one to talk to, millions of Americans facing mental illness don't get adequate treatment. To address the unmet need, experts say, providers must make it easier for people to get behavioral health services in the same place they go for primary care.

Richard Munger, a licensed psychologist in Buncombe County, N.C., says integrated primary care is less threatening for patients with a mental health disorder than going to a separate site for treatment. "In certain models, it reduces or obliterates stigma," he says.

In a May 2010 report for the Milbank Memorial Fund, a health-focused endowment foundation, Munger and other experts laid out different approaches to integrated care. While more providers are starting to incorporate these models, or hybrids of them, Munger adds, collaboration is still a new concept. A snapshot:

1. Improving collaboration: The least integrated model, this first step involves providers at different sites working together, such as a psychiatrist doing phone consults for a primary care practice.
2. Co-location: In addition to diminishing stigma for patients, researchers say collaboration is more likely to be effective if medical providers and mental health professionals are at the same site.
3. Disease management: Because psychological stress and other mental issues often accompany chronic disease, case managers (which can include nurses and master's level social workers) help patients manage both.
4. One treatment plan: Implemented in some federally qualified health centers, this takes co-location a step further, offering primary care and behavioral health services as part of one treatment plan, rather than just side-by-side under the same roof.