There are many treatments available for Hashimoto's thyroidits (autoimmune thyroidits). For this chronic disease, I recommend 100 % gluten free dietary lifestyle, supplementation with selenium and low dose naltrexone. I have been doing this treatment well before there were books written on the subject. I also advocate a cow dairy free dietary lifestyle elimination. The thyroid replacement is usually a natural thyroid such as amour (since hashimoto's) is a t3 deficient state. Sometimes I start with Standard Process Thytrophin PMG. Very rarely do I use the conventional synthroid. I do know that rotating thyroid replacement is beneficial.
Nigella sativa is part of the buttercup family. It is called black cumin. I have used this herb for hyperlipidemia, diabetes, and allergies. In Ayurvedic medicine it is commonly used. It has been shown to improve glucose and lipid metabolism especially insulin resistance or Metabolic syndrome.
Those with Hashimoto's have an increased incidence of insulin resistance so Black cumin is useful. There are antioxidant and anti-inflammatory effects of Nigella.
There is convincing evidence of its use. We know its use as a culinary and medicinal herb is well documented with low toxicity.