Exposure therapy tries to help people who have an overwhelming fear by gradually exposing them to what they fear most, until their Anxiety are partially or totally overcome. This is similar to some allergy treatments, where exposure to small amounts of an allergy causing substance can eventually eliminate the allergy.

Swiss researchers have recently been able to improve the effects of exposure therapy for fear of heights by adding a dose of the stress hormone cortisol. This may sound unusual, since cortisol is a known stress hormone, produced when people are in anxiety-provoking situations. But cortisol also affects learning and memory.

A total score of 120 is maximum anxiety, a score of zero is no anxiety. Study members had an average score of around 59 before treatment. At 3-5 days after treatment, the average score in the cortisol group was 30.4, compared to 40.2 in the placebo group.

According to the researchers, when a phobia like fear of heights is triggered, much of the fear comes from retrieving old memories of how fearful heights were in the past. Cortisol is known to have a general blocking effect on the retrieval of old memories. Blocking recall of old fear memories makes a situation less frightening. Cortisol also aids in the formation of new memories, hopefully here, the memory that heights really aren't that frightening after all.

Whether or not these are the actual reasons cortisol dampened fear in the study, adding cortisol worked better than exposure therapy did alone.

The study was of 40 people with clinically diagnosed acrophobia – fear of heights. Wearing a headset with video glasses, the people were guided through a virtual reality environment – a computer simulated trip along platforms of different heights connected by elevators and bridges. The people were actually standing on a platform six inches above the ground but had the sensation of riding an elevator and making crossings at increasingly greater heights. The final station in the VR environment was reached by crossing a long and narrow bridge connecting two very high platforms.

Half of the people took a 20 milligram cortisol pill one hour before the VR sessions; half took a dummy pill. Subjects were exposed to the simulator for 20 minutes and went through a maximum of 10 stations. Each went through three simulations over the course of one week.

Several different measurements were taken of the effect of this treatment 3-5 days and one month after the last VR session. The two most promising of these were response to a standard fear of heights questionnaire and skin conductance measurements.

The standard acrophobia questionnaire describes 20 situations that can cause fear of heights, such as riding in an airplane, and asks respondents to rate their anxiety of these situations. A total score of 120 is maximum anxiety, a score of zero is no anxiety. Study members had an average score of around 59 before treatment. At 3-5 days after treatment, the average score in the cortisol group was 30.4, compared to 40.2 in the placebo group. One month after treatment, the cortisol group's score was 24.2, the placebo group's was 35.4. This indicates that the VR treatment reduced fear of height and that it worked even better when cortisol was added.

Skin conductance is a measure of how well the skin conducts electricity. It rises when people sweat, as most anxious people do. During follow-up, subjects were given limited exposure to the VR system — a brief simulated elevator ride followed by 60 seconds standing on a virtual roof. While standing on the roof, the measured skin conductance of cortisol group members was less than half of that of control group members, suggesting that the cortisol group was experiencing less fear.

The researchers also report some success at using cortisol to reduce social phobias and fear of spiders. They acknowledge that further studies investigating the effect of cortisol in more challenging real-life situations are needed before the treatment can be deemed effective.

An article on the study was published online ahead of print by PNAS (Proceedings of the National Academy of Science) on March 28, 2011 and will appear in a future print edition of the journal.