I am currently using T3 that is 6 months past it's expiry date - no problems. By the time I reach the end of my stock I expect they will be a year out of date. I don't anticipate a problem, I've read that medication is usually good for at least a couple of years beyond it's expiry date. I think the only thing that might happen is that it could lose some of it's potency and you'd soon know about that.
To store, keep in it's original blister packs/boxes and store in a cool, dry place (not the fridge). Mine are kept in a Lock and Lock box with the little packets of silica gel that come in supplement bottles, and I keep them in a kitchen cupboard that's on an outside wall so it's quite a cool cupboard.
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