Anxiety and depression are prevalent among cancer patients, with significant negative impact. Many patients prefer herbs for symptom relief to conventional medications which have limited efficacy/side effects. We identified single-herb medicines that may warrant further study in cancer patients. Our search included PubMed, Allied and Complementary Medicine, Embase, and Cochrane databases, selecting only single-herb randomized controlled trials between 1996 and 2016 in any population for data extraction, excluding herbs with known potential for interactions with cancer treatments. One hundred articles involving 38 botanicals met our criteria. Among herbs most studied (≥6 randomized controlled trials each), lavender, passionflower, and saffron produced benefits comparable to standard anxiolytics and antidepressants. Black cohosh, chamomile, and chasteberry are also promising. Anxiety or depressive symptoms were measured in all studies, but not always as primary endpoints. Overall, 45% of studies reported positive findings with fewer adverse effects compared with conventional medications. Based on available data, black cohosh, chamomile, chasteberry, lavender, passionflower, and saffron appear useful in mitigating anxiety or depression with favorable risk-benefit profiles compared to standard treatments. These may benefit cancer patients by minimizing medication load and accompanying side effects. However, well-designed larger clinical trials are needed before these herbs can be recommended and to further assess their psycho-oncologic relevance.