Looking for a free, easy and effective way to de-stress? Get outside! Now you've got science on your side. In fact, the results of the study were so convincing, its authors are now providing guidelines to health practitioners to prescribe "nature pills." The authors wrote: "Our study shows that for the greatest payoff, in terms of efficiently lowering levels of the stress hormone cortisol, you should spend 20 to 30 minutes sitting or walking in a place that provides you with a sense of nature."