This is a case study of a 25-year-old female, Ashkenazy Jewish, previously healthy, presented with a complaint of weakness. Her sugar level on the glucometer was 50 mg% and she felt better after ingestion of a small amount of sugar. Two weeks earlier, while traveling in Peru, she developed thyrotoxicosis and began taking Mercaptizol 30 mg a day and Atenolol 100 mg. She didn't drink iodine (iodinated preparations for water purification) while traveling and had no pain or fever. Her physical examination showed no goiter or exophthalmos. While I saw her she was already euthyroid and felt quite good except for fatigue. In the literature, we found a few case reports of Mercaptizol and PTU-induced insulin autoantibodies which cause symptomatic hypoglycemia. Most cases were described in the Asian population (especially Japanese people) and resolved a few weeks after stopping intake of the drug. In our patient, the hypoglycemia resolved after only one episode and discontinuation of Mercaptizol. Insulin antibodies were negative, and insulin levels (C-peptide) were relatively high. My conclusion is that physicians should be aware of Mercaptizol and PTU-induced hypoglycemia which can be life-threatening.