The findings were reported in an article in the journal Thyroid. What the researchers found is that in addition to some of the more commonly known issues with absorption of thyroid hormone (i.e., calcium, iron, and food taken at the same time as thyroid medication can interfere with absorption), coffee also interferes with the intestinal absorption of levothyroxine.
In the study, patients took their levothyroxine (i.e., Synthroid, Levoxyl, Levothroid, Unithroid), with espresso or coffee, and researchers found that the coffee/espresso reduced the rise of the T4 after taking the medication by at least 25% to as much as 57%.
What Should Thyroid Patients Do?
At this point, the evidence is strong enough to suggest that you should not take your thyroid hormone replacement medication with coffee. Ideally, take your thyroid medication, and wait an hour before you have your coffee.
Read more about the interaction between coffee and thyroid medication, what you need to know, and what you can do to protect your health.