I used to use porcine dessicated but whatever they make the pill with wasn't getting digested. I'd see it lol. I use Thyrovanz currently which is bovine. It's more expensive than the stuff I used to get from Thailand but it works great for me. It includes both T3 and T4. Most docs only prescribe one and expect your broken thyroid to manufacture the other which is dumb. And it keeps you having a lot of oddball symptoms they can 'treat'.