It is quite harmful if you suffer from complications of hypothyroidism like I do. My doctor is actually not being overly cautious as I have checked what he told me with other physicians and they have all agreed with my Endo. If you have sleep apnea or any other sleep disorder taking any sleep medication can and will make it worse. If you do not have complications from hypothyroid then I would not know about OTC meds. I am just speaking from experience. Also you mention Prednisone (I take Albuterol for asthma) and cannot take before bedtime as it keeps me awake because it is a stimulant.