 The most common side effect of low-dose nalfurafine seen in clinical trials was insomnia (observed in 10–15% of patients), with few other adverse effects observed.In addition, tolerance to the antipruritic effects of nalfurafine was not found after treatment of patients with the drug for one year, and nalfurafine has shown no evidence of either physical nor psychological dependence in humans.The drug also shows lower evidence of tolerance for effects such as analgesia and sedation in animals relative to other KOR agonists.