I believe that the thyroid can become underactive during periods of stress when the adrenal glands are under extra pressure. I was in a very stressful relationship some 20 years ago and went to the doctor with terrible tiredness. My thyroid levels were checked and I was found to be borderline underactive. (as there's no definitive marker for under or over I can't understand how someone can be 'borderline'! but still) I was immediately put on to 100 microgram’s of Levothyroxine and then subsequently increased to 150mg which actually gave me chest pains. I have since gradually decreased the dosage to 50mg. (with my doctors agreement) I believe that if my doctor had waited and maybe asked a few questions as to my emotional state at the time, my thyroid could have been given the chance to recover. (once I got out of the relationship) Now of course because I've been on the drug for so long, I know that my thyroid would have stopped producing the hormones so I have to stay on the drug forever. I believe doctors should use caution when prescribing for a borderline underactive thyroid. It may just recover on it’s own.