Follicular adenoma is not a cancer, but can cause some problems if left to grow. Mine was pressing quite severely on my trachea making it hard to swallow and breathe. Removal is the only answer.
The doctor he should see is an ENT or Otolaryngologist (same thing). They are ear, nose and throat specialists and surgeons. He should also see an experienced one, the thyroid is a delicate gland and much can go wrong with an inexperienced surgeon. No, it cannot be cured with medication, it will not go away, sometimes they can shrink it slightly, but it can't be cured. Usually he has only a 5-15 % chance of cancer, it is probably benign, but he should investigate it further. How big is it? Vascular? Solid or Cystic? Is it causing symptoms? He can live just fine without a thyroid, most of us do.