The Effects of Taking too Much Thyroid Hormone Replacement

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Thyroid hormone replacement drugs generally have few side effects. And for someone who has hypothyroidism due to disease, surgery or radioactive iodine, there are few risks to properly taking thyroid hormone replacement drugs (levothyroxine drugs like Synthroid or Levoxyl, a T3 drug like Cytomel, or a natural desiccated thyroid drug like Armour or Nature-Throid). The most common "risk" or "side effects" of these drugs, however, are symptoms due to overmedication.

Many doctors will attempt to use your thyroid blood test results to assess whether you are getting too much medicine. In some people, TSH levels at the lower end of normal, or below the low-end of normal (i.e., below 0.3 to 0.5) may trigger symptoms of overmedication. Some doctors also monitor T4 and T3 levels -- results indicating that you are at the high end of normal or above the normal range may point to overmedication.

Some practitioners also use elevated pulse rate. Pulse can be very sensitive to thyroid medication dose in some people, so it's a way to tell if a patient is overmedicated.

What Are the Signs and Symptoms of Overmedication? 

Some patients who are hypothyroid -- whether due to disease, surgery or radioactive iodine ablation -- can become overmedicated.

Signs and symptoms vary, depending on the person, but signs of overmedication with thyroid hormone replacement are often similar to the symptoms of hyperthyroidism, and can include:

  • Elevated pulse and blood pressure
  • Anxiety, nervous energy, tremors, feeling jittery
  • Shaking hands, tremors
  • Feeling irritable, overemotional, aggressive, easily startled, or erratic
  • Difficulty concentrating, mind is always racing, can't shut off thoughts
  • Difficulty sleeping, insomnia
  • Fatigue, exhaustion
  • Perspiring, feeling overheated, especially when others are cold
  • Diarrhea or loose bowels
  • Heart palpitations, feeling like heart is skipping a beat, or racing
  • Depression
  • Weight loss with no change to diet/exercise, or sometimes, paradoxically, weight gain
  • Increase in food intake, with no weight gain
  • Craving and/or eating more carbohydrates (bread, rice, pasta, sweets, fruits, sugary foods, etc.)
  • Unusual hunger pangs
  • Excessive thirst
  • Loss of appetite
  • Diarrhea, or frequent bowel movements
  • Hair loss
  • Changes to menstrual period (lighter, less frequent)
  • Enlarged, sensitive or tender neck
  • Dizziness, breathlessness
  • Achy or weak muscles and joints
  • Eyes are enlarging or looking "bug-eyed"
  • Dry, gritty, irritated, red eyes
  • Headache in eye area, pain behind the eyes

Sometimes, it's hard to recognize the signs of overmedication. You might assume that if you are overmedicated, you should feel the opposite of your symptoms when hypothyroid; and that taking too much medication will make you feel energetic, or that you'll lose weight, and feel great. So, when you start to feel even more exhausted than usual, or achy and almost flu-like, or you even start gaining weight despite feeling jittery and anxious, you may not suspect that you are actually overmedicated.

In fact, you might go to the doctor to get tested, sure that you are hypothyroid and require an increase in dosage, only to find out that the symptoms you're experiencing are actually due to overmedication.

How Do You Become Overmedicated? 

There are a number of ways you can become overmedicated.

  • The dosage of thyroid hormone replacement that your doctor prescribed may be too high for you. Sometimes, doctors overestimate the dosage you will require to return to normal status and resolve symptoms.
  • You may get an incorrect batch of medication. Pay particular attention to symptoms that develop after a recent pharmacy refill. Your pharmacist may have made a mistake in your medicine dosage.
  • If you are taking generic levothyroxine (which most doctors do not recommend), in your last refill, you may have gotten a more potent batch. Even the slight change of potency from one refill to the next, particularly from one manufacturer of generic levothyroxine to another, can be enough to push you into hyperthyroidism.
  • You may have started taking an over-the-counter supplement that includes animal thyroid (pay particular attention to "thyroid support," energy support and diet aids that include ingredients like "thyroid glandulars" or "adrenal glandulars" or "bovine glandulars" -- as these can introduce extra thyroid hormone into your system and make you hyperthyroid.
  • You may be taking over-the-counter supplements that contain iodine, bladderwrack (fucus vesiculosus), kelp, bugleweed, Irish moss or seaweed. Too much iodine can aggravate the thyroid in some people.
  • You may have recently changed your diet, affecting your absorption of thyroid hormone medication. For example, if you were eating high-fiber, and cut back on the fiber, you may be absorbing higher levels of thyroid medication. Be sure to take your thyroid medication properly.
  • You may have recently stopped supplementing with iron or calcium. Since both substances can interfere with thyroid hormone absorption in some people, stopping them may increase the amount of thyroid available for absorption.
  • If you've just lost a substantial amount of weight, but haven't changed your thyroid dosage, you may be getting too much medication.
  • If you've just had a baby, the increased need for thyroid hormone during pregnancy drops, and the amount of thyroid hormone replacement you needed during pregnancy can become too high for the post-partum period, causing hyperthyroidism.
  • If you've just had a baby, post-partum thyroid fluctuations may cause your thyroid to over-function periodically, so the thyroid's own hormone production, when added to your thyroid hormone replacement, is temporarily causing hyperthyroidism.
  • If you have Hashimoto's Disease, you may be in a period of fluctuation where the thyroid is over-functioning and the thyroid's own hormone production, when added to your thyroid hormone replacement, is temporarily causing hyperthyroidism.

Treatment for Overmedication

Typically, the "treatment" for overmedication is to cut back the dosage, until blood test levels return to more normal levels, and overmedication symptoms are eliminated. Your doctor should retest you and re-evaluate your symptoms frequently until your dosage and levels are stabilized, and the overmedication is resolved.

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