Does Lugol's Iodine expire after it's been opened?

I bought 2 - 1 liter bottles of Lugol's Iodine a couple of years ago. One is opened and one is not. I stopped using Iodine for whatever reason I can't remember, but want to start again. Does it actually expire/go bad? And how could I tell. I think the unopened one is okay, but what about the one that is and what's the worst that could happen if it is expired? Does it lose its potency or could it actually make me sick?

I hate to just throw it out if it's still "good."

Thanks