For the Lugol's Spud mentioned, J Crow's is a reputable source. 5% Lugol's is 6.25 mg per vertical drop; 8 drops gives 50 mg; 16 drops gives 100 mg. On the order form, it's EX 102. Some people take 2% Lugol's. Multiply doses by 2.5 to get the equivalent amount of iodine listed for the 5%.
If you prefer tablets, they're more expensive. Depends on your preference. Some people have stomach irritation taking Lugol's, but hard to predict. One Iodoral 12.5 mg tablet = 2 drops Lugol's 5% = 5 drops Lugol's 2%. Eight Iodoral = 100 mg. The tablets are easy to split in half. There is a larger 50-mg tablet which you can switch to after you're sure you can handle it.
As for side effects, generally newbies are faced with bromine detox. Many, many posts discuss this. That's because the iodine starts taking it's rightful place in various receptors, booting out the bromine interlopers. Rougher for some than for others. Yes, it's worth it. Read, read, read. To get you started --