貫葉連翹藥力強大，可能與其他西藥互相牴觸，例如降低避孕藥療效，故服用前應諮詢醫生意見。其副作用較西藥低。常見副作用包括腸胃不適、頭暈、混亂、疲倦、鎮定、口乾、煩躁及頭痛。其他可能導致光照性皮炎。對躁鬱症患者可能會誘發躁症而精神分裂症患者可能會惡化其幻覺。
St. John's wort is powerful and may conflict with other Western medicines, such as reducing the efficacy of contraceptives, so you should consult your doctor before taking it. Its side effects are lower than those of Western medicines. Common side effects include gastrointestinal upset, dizziness, confusion, tiredness, calmness, thirst, irritability and headache. Others may cause photodermatitis. Bipolar disorder may be induced in people with bipolar disorder, while hallucinations may be exacerbated in people with schizophrenia.