Its a combo of T4/T3...it is glandular from pig like Armour but more pure. It has all the thyroid hormones in it. I use a pill cutter and take 1/8 grain at night because it helps me sleep for some reason but most people take theirs in the am because the T3 is active and may cause insomnia in large doses because it gives you energy but for me it helps me sleep. I get it from my doctor at Gerber medical center in Reno Nevada.