Serious side effects of statins, including severe myopathy and rhabdomyolysis, 
are rare but important in general practice. Hypothyroidism can cause secondary 
hypercholesterolemia and myopathy. There have been few reports on the risk of 
statins in patient with unnoticed hypothyroidism. We analyzed the 
characteristics of 77 patients with primary hypothyroidism in our hospital. Nine 
patients (11%) accidentally received statins in the treatment of 
hypercholesterolemia without diagnosis of hypothyroidism. In such patients, free 
T4 (FT4) levels were lower, and those of LDH, CK were higher than those in 
patients not receiving statins. In patients accidentally receiving statins, an 
inverse correlation between CK and FT4 could not be shown (which was recognized 
in patients not receiving them). Even after FT4 levels were matched, levels of 
CK were still higher in the patients accidentally receiving statins. Patients 
with high CK levels over 1000 U/L were 5 times more frequent (56%) in patients 
accidentally receiving statins than in those not receiving statins (11%). The 
present study confirms that statins enhances levels of CK in patients with 
hypothyroidism. We must not begin and continue to use these drugs without 
checking the possibility of hypothyroidism.