If you have an overactive thyroid, you should check with your healthcare professional before taking CoQ10. CoQ10 is helpful for under-active thyroids, for it stimulates the thyroid to work more efficiently. Because safety of CoQ10 during pregnancy and lactation has not been clinically proven, Q-Gel CoQ10 should not be used during this period except under the advice of a healthcare professional. There are no other known conditions for which CoQ10 is unsafe to ingest.