Can a hypothyroid person safety use apple cider vinegar?

Yes: There is no biochemical pathway for apple cider vinegar to interfere with any of the replacement meds. However, there is some anecdotal, albeit unproven data that apple cider vinegar helps with some of the digestive issues of hypothyroidism and helps with weight gain. The scientific data for this is sketchy though, and view with caution. But yes, you can ingest it safely.