T Nation

T3 Half-Life?

I get ranges all over the place on the half-life of T3: anywhere from 7 hours to ~2.5 days. Now, I’ve had some people tell me that their pharmaceutical package insert said 2.5 days half-life, yet others swear that it’s more like 7-10 hours. I’ve read medical sites that quote a 1 day half-life. What the hell’s going on here? Why is the half-life of T3 so hard to pin down, does it really vary that much?

I’m trying to figure out if there is really any need to split the dosage during the day.



It is wise to split the dose yes. Most hypothyroid sufferers will split the dose by eight hours roughly; early am and mid afternoon. You should feel the t3 peak at roughly 3 - 4 hours or so, and taper off after that. As you say, half life data seems contradictory. If you were a patient and you were to have a routine blood test, you would likely be advised to not have a dose for 24 hours prior to the test.

When I was on T3 (thyroid cancer), the doctor has me taking it once a day.