Complex sentence: Only a single double-blind, placebo-controlled study has examined the effectiveness of "R. rosea" as a monotherapy for depression, however, patients treated with "R. rosea" extract showed a reduction in depressive symptoms compared to patients treated with placebo.
Split into simpler sentences: Only a single double-blind, placebo-controlled study has examined the effectiveness of "R. rosea" as a monotherapy for depression. In that, patients treated with "R. rosea" extract showed a reduction in depressive symptoms compared to patients treated with placebo.