A red clover (Trifolium pratense) phase II clinical extract possesses opiate activity

Trifolium pratense (TP) is one of the most common herbs for the relief of menopausal symptoms. Little is known about its mechanisms of action. In this study, we investigated the affinity of TP at the μ- and δ-opiate receptors. We found that a clinically used TP extract bound to the μ-opiate receptor with a high affinity (Ki = 9.7 ± 1.6 μg/ml). The same extract was also found to have affinity at the δ-opiate receptor with Ki of 15.9 ± 2.4 μg/ml. These results for the first time suggest a potential new mechanism of action of TP at the opiate receptors. Given the essential role of the opioid system in regulating temperature, mood, and hormonal levels and actions, this may explain in part the beneficial effect of TP in alleviating menopausal symptoms.