Randomized Controlled Trial of Dolphin-Assisted Therapy in the Treatment of Depression

 

Objective

To investigate whether dolphin-assisted therapy is more effective than exposure to a natural aquatic environment alone in the treatment of mild to moderate depression, within the framework of the biophilia hypothesis.

 

Study Design

• Single-blind, randomized, controlled trial

• Conducted in Honduras

• Participants recruited in the United States and Honduras

• 30 patients with mild to moderate depression​

 

Method

Participants were randomly assigned to one of two groups:

 

1. Dolphin Group (Animal Care Programme)

• One hour of daily interaction with dolphins

• Structured component (touching dolphins, trainer-guided activities)

• Unstructured component (free snorkeling with dolphins)

 

2. Control Group (Outdoor Nature Programme)

• Same natural environment

• Same water-based activities (swimming, snorkeling)

• No dolphins

 

Both programs lasted two weeks (Monday–Friday, one hour per day).​

 

Assessment Measures

• Hamilton Depression Rating Scale (HDRS)

• Beck Depression Inventory (BDI)

• Zung Anxiety Scale

 

Clinically significant improvement was defined as:

• Hamilton score ≤ 7

       or

• ≥ 50% reduction in depression score​

 

Results

Of the 30 participants:

• 2 dropped out of the dolphin group

• 3 withdrew from the control group

 

Depressive Symptoms

The dolphin group showed a significantly greater reduction in depressive symptoms than the control group:

• Hamilton: p = 0.002

• Beck: p = 0.006

​​

This difference remained significant in the intention-to-treat analysis.

 

Clinically Significant Improvement

• 77% of participants in the dolphin group achieved clinically significant improvement

• 25% of participants in the control group achieved clinically significant improvement

 

After adjusted analysis:

• 67% versus 20%

 

Anxiety

Both groups showed improvements in anxiety symptoms, but the difference between groups was not statistically significant.

 

Interpretation

The study concluded that:

• Dolphin-assisted therapy is more effective than water-based therapy alone for individuals with mild to moderate depression.

• The natural environment itself has a therapeutic effect, but the effects produced by the animals were significantly greater.

 

Possible explanations include:

• The dolphins’ echolocation system

• The aesthetic value of the interaction

• The emotional response elicited by contact with the animals

 

The authors suggest that sensory stimulation of the nervous system may play a role.

 

Time to Effect

Improvement was observed within two weeks.

 

For comparison, conventional treatments (medication and psychotherapy) often do not show clear improvement until after four weeks.

 

No adverse effects were reported.

 

Limitations

• Participants could not be blinded to treatment allocation

• Selection criteria were strict

• No long-term follow-up was conducted

 

However, many participants reported continued improvement three months later.

 

Conclusion

The biophilic intervention method—interaction with animals in a natural environment—may represent an alternative clinical strategy for emotional disorders.

​

Psychological recovery may occur through:

• Emotional engagement

• A holistic experience

• Psychophysiological stimulation

• Sensory activation

 

The study emphasizes that our psychophysical health is closely connected to our relationship with the natural environment.