Researchers took a look at some of the key factors that cause patients to need larger-than-expected dosages of thyroid medication. The study looked at levothyroxine dosages in hypothyroid patients, but the factors they identified - the reasons why you may need more thyroid medication - are relevant whether you're taking levothyroxine, liothyronine (T3), or natural desiccated thyroid for your hypothyroidism.
Reason 1: Your Medication is Impairing Absorption
One key factor that may cause you to be on a higher dose is that you are taking a medication that is known to interfere with thyroid medication absorption.
In the study, 21% of the patients were taking a drug that interfered with absorption of their thyroid medication.
Reason 2: You Have Undiagnosed Celiac Disease
In the research, study members were tested for anti-endomysial antibodies and evidence of celiac disease. As many as 4% of the study population was found to have undiagnosed celiac disease. (It's estimated that 2 to 5% of autoimmune thyroid patients have celiac disease — substantially more than the estimated 1% of the population with celiac disease.) Celiac disease affects the body's ability to properly absorb thyroid medication thoroughly.
Reason 3: You Have Autoimmune Gastritis
For patients with autoimmune thyroid disease, it's more common to also have another autoimmune condition, called autoimmune gastritis. To diagnose this condition — which affects and impairs absorption in the gut — you're tested for parietal cell antibodies (PCA).
In the study, 22% of the patients had parietal cell antibodies that were causing them to require higher doses of thyroid medication.
Reason 4: You're Not Compliant
Doctors use the term "non-compliant" to describe patients who are not taking their medication properly, or at all. In the study, 17% of those studied had "compliance issues," defined as taking their medication improperly, or missing at least one dose of thyroid medication per week.
Some patients drink coffee, and do not wait at least an hour to take their thyroid medication. Others eat, and again, don't wait at least an hour before taking their medication. Some patients reported taking their medication with calcium supplements, calcium-fortified juice, or along with iron supplements.
The other category of non-compliance is simply not taking the medication, typically at least once or more a week. The reasons people miss a dose are varied, but typically they simply forgot, didn't have symptoms that day (and erroneously decided not to take their thyroid pill), or had eaten and didn't want to take it on a full stomach.
Source: Robertson Hannah M.A., Narayanaswamy Anil K.P., Pereira Olivia, Copland Shirley A., Herriot Richard, McKinlay Alistair W., Bevan John S., and Abraham Prakash. Thyroid. December 2014, 24(12): 1765-1771. doi:10.1089/thy.2013.0661. Published in Volume: 24 Issue 12: October 27, 2014 Abstract