Yes, it is. Your GP can prescribe thyroid glandular for you - Armour brand is considered to be the most reliably standardized one available. Before synthetic thyroid hormones were created by pharmaceutical companies, everyone who had low T4 and/or T3 was prescribed with these kinds of freeze-dried raw animal thyroid gland products. Most doctors prescribe the synthetic T4 products for low thyroid functioning, but in recent years the importance of the T3 thyroid hormone has been becoming more evident to patients, who feel better when taking both. Natural thyroid (freeze-dried glandular products such as Armour) have both the T4 and T3 hormones in the perfect mix. It is not surprising that you feel much better taking a glandular product given that your T4 levels were low. If your doctor had ordered tests to check your T3 levels, they would in all likelihood been low as well. Most of T3 hormone converts to T4 hormone in the body, over time, which is why most doctors do not consider it important. However, before the T3 hormones convert to T4 they produce a wonderful feeling of vitality and wellbeing. The only reason that the natural (glandular) thyroid products lost favor with the medical community, is that it is more difficult to ensure that the companies producing these freeze-dried animal products are doing a good enough job standardizing (making sure the products are always exactly the correct strength). I take Armour brand thyroid and have never had any kind of problem. I much prefer this natural form of thyroid to the synthetics, and my doctor is happy to prescribe it for me.