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For many patients, like Lauren Huddle, 31, a big dose of Mother Nature is exactly what she needs after a stressful day.

“I have pretty bad anxiety and depression,” said Huddle of Bellingham, Washington. “And I don't do well with pharmaceuticals, so my husband Nate would actually tell me all the time, ‘just go outside, you'll feel so much better.’"

And that’s exactly the plan that Lauren and her doctor laid out.

The Huddle’s family physician wrote her a prescription that read: “Five times a week… spend 30 minutes at a park near your home.”

Huddle's treatment plan is part of a growing field of medicine called "ecotherapy" — nature-based programs and exercises that can help patients cope with mental and physical illnesses. Instead of prescriptions for more pills, doctors around the country are increasingly prescribing trips to the park for a range of conditions, including anxiety and depression, attention deficit disorder and chronic illness such as diabetes and high blood pressure.

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“We work with the doctors, nurses, and health care providers around the country and show them why it’s so relevant to prescribe parks and how easy it is to do, so that they can make it a part of their daily routine,” said Dr. Robert Zarr, medical director of the nonprofit Park RX America and Unity Healthcare, a Washington, D.C. group that coordinates with managers of public lands and over 50 doctors in 11 states.

The healing power of nature

There's plenty of evidence of the healing power of a walk in the woods. “Forest bathing,” a version of the Japanese practice Shinrin-Yoku, is taking off in American as a way to boost happiness and help with insomnia. And scientists have long studied how going into nature changes the way the brain works.

Researchers at the University of Essex found that 9 out of 10 patient suffering from depression felt "higher self-esteem after a walk through a park." Almost three-quarters reported feeling less depressed and the researchers found that people recovered faster from illnesses through an 'immunizing' effect that protected them from future stresses.

Related: This digital pill will track your psychiatric meds

During ecotherapy, which combines nature walks with therapy sessions and simple exercises, patients are instructed to focus on three key elements:

The sounds of chirping birds

The visuals of trees and leaves

and the sound of streams or rivers

"We write prescriptions for all kinds of medicines. In addition to that we're starting to see nature and parks, not just as a place to recreate, but literally as a place to heal yourself," Zarr said.

Huddle got her prescription just three weeks ago and has already begun to see the positive effects.

"Just going out there, little bit by little bit, I noticed my temperament was better and my anxiety started to greatly decrease," said Huddle.