Results of routine thyroid function tests in heavy cocaine abusers at the time of treatment admission were not statistically different from normal values for our laboratory or from a similar group of other substance abuse patients in treatment. This suggests that heavy cocaine use per se does not affect thyroid function. Therefore, if the thyroid function tests are abnormal in a cocaine abuser, then a true thyroid dysfunction should be considered and completely evaluated. In addition, nonspecific alterations in thyroid function tests in nonthyroidal illnesses should be kept in mind.