Comparing The Different Types of Antithyroid Medications
Published February 13 2017
Many people with hyperthyroidism and Graves’ Disease take antithyroid medication. And while these prescription drugs don’t do anything to address the cause of the condition, if someone is experiencing cardiac symptoms such as an elevated resting heart rate then it is important to manage these symptoms. Plus, elevated thyroid hormone levels can also have a negative effect on bone density. While it is true that there are natural herbs such as bugleweed that can help to decrease thyroid hormone production, for some people, the herbs aren’t potent enough to accomplish this. And so the goal of this article is to discuss some of the different types of antithyroid medication.
But before I talk about the different types of antithyroid medication, I’d like to briefly discuss some basic information about these drugs. First of all, antithyroid medication blocks the formation of thyroid hormone. As a result, when taking antithyroid medication you should see both the T3 and T4 levels decrease, and eventually the TSH will increase in response to this. As for the dosage someone needs, this does depend on the person, as some people will need to take higher doses, while others might do fine with a lower dosage. In most cases you will need to take antithyroid medication for at least three weeks to lower thyroid hormone levels, but it can take longer than this (1). And the reason for this is because these drugs only block the formation of new thyroid hormone that is produced, and don’t remove thyroid hormone that is already in the thyroid gland and blood stream (1).
So let’s go ahead and discuss three of the main types of antithyroid medication:
1. Methimazole. This is the most commonly prescribed medication for hyperthyroidism in the United States. It’s also known as Tapazole, which is the brand name of Methimazole. Methimazole works by inhibiting the enzyme thyroperoxidase, which plays an important role in the synthesis of thyroid hormone. If someone has a severe case of hyperthyroidism then they typically will start off with a higher dosage of Methimazole (i.e. 40 to 60 mg/day in divided doses), whereas someone with a milder case will take anywhere from 5 to 20 mg/day. The inactive ingredients include lactose monohydrate, magnesium stearate, corn starch, pregelatinized starch and talc (2). The lactose is a very small amount and usually isn’t problematic for those who have a mild to moderate lactose intolerance, although if someone has a corn allergy then they might react to the medication due to the corn starch.
2. Propylthiouracil (PTU). This is less commonly recommended for hyperthyroidism, and the main reason is because it puts more stress on the liver, which I’ll talk about in greater detail shortly. But I will say that if someone is taking any type of medication it is a good idea to monitor the liver enzymes through a comprehensive metabolic profile, and this is especially true for anyone taking PTU. PTU not only inhibits the thyroperoxidase enzyme, but it also inhibits the enzyme 5′-deiodinase, which is involved in the conversion of T4 into T3. Just as is the case with Methimazole, the recommended dosage will depend on the severity of the condition, as the dosage for adults will range between 100 mg and 300 mg per day. The inactive ingredients include corn starch, docusate sodium, magnesium stearate, microcrystalline cellulose, pregelatinized starch, sodium benzoate, and sodium starch glycolate (3).
3. Carbimazole. This drug is more commonly recommended in other countries, and it converts into Methimazole. The dosage can range from 5 mg for milder cases, to 40 mg for more severe cases. The inactive ingredients include lactose, corn starch, sucrose, magnesium stearate, talc, gum acacia, ferric oxide, and gelatin (4).
What Are The Side Effects Of Antithyroid Medication?
While many people do fine taking antithyroid medication, drugs such as Methimazole and PTU commonly cause side effects. Here are some of the side effects associated with these medications:
- Elevated liver enzymes
- Depressed white blood cells
- Skin rashes
- Joint and muscle pain
- Hair loss
Choosing Between Methimazole and PTU
In the United States Methimazole is more commonly prescribed over PTU. This is also true in other countries, as whenever an endocrinologist recommends antithyroid medication, either Methimazole or Carbimazole are usually prescribed. And the reason for this is because PTU is harsher on the liver, and thus is more likely to cause elevated liver enzymes. However, if someone doesn’t respond well to Methimazole or Carbimazole, then PTU very well might be prescribed. So for example, if someone has an allergic reaction to Methimazole, then PTU might be prescribed. And while there is the chance that the person will react with to both Methimazole and PTU, this isn’t always the case. It depends on the situation, as if someone is allergic to corn, then they are likely to react to both Methimazole and PTU since they both have corn starch.
Another scenario in which PTU is commonly prescribed is during the first trimester of pregnancy. And the reason for this is because Methimazole is more likely to cause malformation of the fetus (5). As a result, most endocrinologists will recommend for their pregnant patients with hyperthyroidism and Graves’ Disease to take PTU during the first trimester, and then will usually switch them to the Methimazole during the second and third trimesters.
What Are Some Natural Antithyroid Agents?
I’m not going to get into detail about natural antithyroid agents, as I have some articles and blog posts on my website that get into greater detail. Bugleweed is the antithyroid herb I commonly recommend for hyperthyroidism, and for more information I would check out the blog post entitled “Which Are The Best Herbs For Managing The Symptoms Of Hyperthyroidism and Graves’ Disease”. In this blog post I also talk about lemon balm, which has some mild antithyroid activity. L-carnitine and lithium also can inhibit the production of thyroid hormone.
Should YOU Take Antithyroid Medication?
When I was dealing with Graves’ Disease I chose not to take antithyroid medication, as I was able to use the herbs bugleweed and motherwort to manage my symptoms. However, not everyone can successfully manage their symptoms naturally, and many of my patients do take antithyroid medication while trying to address the cause of the problem. While it’s great to be able to avoid taking medication, being safe should be the number one priority. In other words, everything comes down to risks vs. benefits, and in most cases the risks of unmanaged hyperthyroidism is greater than the potential risks of taking antithyroid medication. Of course there are exceptions, as if the medication causes elevated liver enzymes or other side effects then this is definitely a concern, but many people take antithyroid medication without experiencing these problems.
In summary, managing the hyperthyroid symptoms is important, and many people choose to do this by taking antithyroid medication. The three main types of antithyroid medication are Methimazole, PTU, and Carbimazole. These all block the formation of thyroid hormone. In the United States Methimazole is more commonly prescribed, as PTU puts more stress on the liver. With regards to antithyroid herbs, bugleweed is the one I commonly recommend, and is the one I personally took when I was dealing with Graves’ Disease.