Hi Dawn, There are no current studies comparing the effects of cod liver oil and fish oils on thyroid medications.

Did you know that one of the possible side effects from fish oils include an increased risk for bleeding?

Incidentally, one of the possible side effects from taking Synthroid (levothyroxine) is it may increase the effects of blood thinners such as Warfarin or Coumadin. Therefore, if you take fish oils and sythroid at the same time, you may increase your risk for bleeding.

It's always important to consult with your physician before taking any nutritional or dietary supplement; especially if you're taking any type of medication. This will help you avoid possible side effects and negative interactions that might occur.

Here's more information from other visitors that have asked about side effects from using fish oils and thyroid medications.

Good luck and I hope this information is helpful.

Thank you for your comments. They certainly make sense. I've told my doctor the same thing but she makes no comment. Frustrating! I worked for as a doctor's nurse and I have always tried to learn new things to help people. I think this is one for the drug reps to take home to the manufacturer. I have always known that you shouldn't take thyroid meds with food but have always done it with no problems for over 10 years. However I think i've found the food (fish oils) that you don't take it with! (Maybe even flax)