In this study, we report a case of a 50-year-old Japanese man who had chronic whiplash-associated disorder, hyperlipidaemia, hyperuricacidaemia, and mild liver dysfunction due to excessive alcohol intake. Recently, he developed mild tremor in his left hand. Initiation of clonazepam (0.5 mg once daily before bedtime) helped to gradually ameliorate the tremor. However, 13 days after clonazepam initiation, his liver function and lipid profiles aggravated, and his postprandial glucose level increased to 400 mg/dL. Clonazepam was stopped promptly, and at 7 days after discontinuation, the abnormal triglyceride levels, liver dysfunction, and glycometabolism improved without any other medical intervention. This case may provide information on cautious use of clonazepam. When clonazepam is used for patients with existing hyperlipidaemia and liver dysfunction, it may cause abnormal lipid profile, aggravate liver dysfunction, and lead to remarkable glucose elevation.