A safety study in humans has shown that 7-KETO did not raise estrogen or testosterone levels or produce any other negative effects at levels up to 200 mg per day for eight weeks.³ Short-term animal studies also revealed no adverse effects with large amounts of 7-KETO.^{4, 5, 6} However, the long-term safety of 7-KETO for humans has not been demonstrated, and, because it is chemically related to steroid hormones, the potential for adverse effects must be considered. In addition, the increase in T3 levels resulting from taking 7-KETO could, in theory, produce adverse effects on the heart or promote bone loss. For these reasons, people wishing to take 7-KETO, particularly those who have a thyroid disorder or are taking thyroid hormone, should consult a physician.