There are a few common supplements that have a known issue with affecting levothyroxine absorption. Calcium salts as well as other metal containing containing substances such as iron, aluminum and magnesium can greatly decrease levothyroxine absorption. A decrease in levothyroxine absorption can affect your thyroid levels, which could potentially cause your hypothyroidism to not be appropriately treated.

Most vitamins and supplements contain some type of ingredient (e.g. calcium) that can affect levothyroxine absorption. Therefore, if you are taking a supplement or vitamin, it is generally recommended to take it at least four hours after taking levothyroxine to avoid this interaction.


Levothyroxine is a synthetic T4 hormone used in the treatment of hypothyroidism. Common side effects associated with taking levothyroxine include but are not limited to:

  • Insomnia
  • Weight loss
  • Tremor
  • Upset stomach

Levothyroxine should be taken first thing in the morning, 30 to 60 minutes prior to eating breakfast or taking any other medication. It should be taken with a full glass of water to prevent choking and or gagging on the tablet.

It is important to note that if you have been taking this medication a different way or time, you should continue to take it in that manner. The most important part of levothyroxine administration is taking it the exact same way and time everyday.

Levothyroxine is a potent medication, that is dosed in micrograms, not milligrams. A small change is how much medication is absorbed or make a huge difference in effect. Therefore, consistency is key with levothyroxine dosing.