I think thyroid and other hormone reactions are entirely dependent on the state of the liver and gut, which can vary a great deal with antigenic burden, bacterial counts, endotoxic insult, metabolic stress and the damage that results from lactic acid, free fatty acids and prostaglandins (to name a few).
I think Peat talks about this in his articles, but to me it seems largely undervalued here and in the forum. Just recently, Jennifer asked Peat about thyroid use and mood swings, for example, and Peat wrote back that thyroid should not be used when the liver and gut are not up to it.
I typically write that the liver and gut can be regenerated without the necessity of thyroid or hormones, if you can:
1) Exercise at high altitude and get plenty of daylight (or emulate those conditions);
2) Keep to extremely minimal fats and avoid starch antigens by drinking pulp-free orange juice, especially if you are likely to have fatty liver or digestive issues; (check your BMI, waist circumference, triglycerides and GGT: http://www.biomedcentral.com/content/pdf/1471-230X-6-33.pdf)
3) Use raw carrot, coconut oil, activated charcoal, tetracyclines or cascara to reduce antigenic burden, bacterial counts and endotoxic insult;
4) Experiment to find a balance of Peatarian nutrients that is unique to you (especially aspirin, coffee, urea, magnesium bicarbonate, sodium chloride, thiamine, niacinamide and the other B vitamins, and Vitamins A, D and K/K2).
I'm frequently criticized, perhaps rightly so, for being overly didactic. I do agree that steps 1 and 2 are didactic in nature.
But in steps 3 and 4, I think each person needs to find his or her own digestive and nutrient balance in an ever-changing world of metabolic stress. Thyroid and the other hormones may only be needed in the context of this balance.