Outdoor therapies delivered by mental health professionals: A scoping review of clinical trials.

BACKGROUND

Outdoor therapy is a rapidly expanding practice but remains outside mainstream psychotherapy. It is unclear which clinical trials have been conducted, with which populations, and their methodological quality. This review aimed to identify published trials of outdoor therapy delivered by licensed therapists and summarise intervention modalities, characteristics, facilitator qualifications, targeted populations, and mental health presentations.

METHODS

Five databases were systematically searched using keywords for identified outdoor therapy interventions (e.g., adventure therapy, nature-based therapy), supplemented by forward and backward citation searches. Eligible studies included pre-post measures of at least one outdoor therapy intervention facilitated by a mental health professional. Data were extracted on modality, setting, intensity, facilitators, participant characteristics, outcomes, and risk of bias appraised via the Joanna Briggs Institute checklist.

RESULTS

Of 7393 records screened, 63 studies met inclusion criteria: 13 randomised controlled trials, 50 quasi-experimental designs. Over half (60%) targeted clinical populations (e.g., depression, PTSD, substance use), with others involving veterans, employees, or healthy adults. Common modalities included nature-based (32%), adventure (29%), forest (19%), horticultural (13%), and wilderness therapy (8%). Most were delivered in public natural spaces, and half were co-facilitated by mental health professionals with non-therapists. Outcomes commonly targeted stress, anxiety, depression, and quality of life, while nature-specific outcomes were assessed in only 14% of studies. Methodological risk of bias was mixed, many studies were not pre-registered.

CONCLUSIONS

Outdoor therapy research spans diverse populations and settings but remains methodologically heterogeneous. Advancing the field requires adequately powered, pre-registered trials with standardised outcomes to clarify efficacy and mechanisms.