What are the real powers of aromatherapy? Systematic reviews of clinical trials give us an even better picture than single clinical trials.
In January 2017, a systematic review was published of 12 randomized clinical trials which had studied the effectiveness of aromatherapy in alleviating depressive symptoms. In five studies inhalation was used, and seven employed massage. One conclusion of the review was that aromatherapy massage was more effective than EO inhalation, using comparable rating scales. This is not surprising – two of the studies found massage with plain carrier oil had an effect, though when aromatherapy was used as well the effect was significantly greater.
In conventional drug research, the placebo effect for depressive symptoms is typically 30-40% https://www.ncbi.nlm.nih.gov/pubmed/7945737 and this review showed an average efficacy of 58%, so way above that threshold.
Various essential oils were used in the studies, and the most frequent ones included Lavender (9 studies), Rose otto (4 studies), Geranium (3 studies), Bergamot (3 studies) and Rosemary (2 studies).
The review concluded that aromatherapy shows potential as an effective therapeutic option for the relief of depressive symptoms. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5241490/
Clinical depression is a complex disorder with varied etiology, and it would still be a stretch to claim that any single essential oil works as a general anti-depressant. However this systematic review confirms that aromatherapy shows great promise as a complementary therapy for depressive states. The review did not look at mood-enhancing effects, which are measured differently to those for depression.