Should You Take Generic Levothyroxine?

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Generic levothyroxine is as safe and effective as brand names, but patients need to be careful about potency variations.. istockphoto.com

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4). It is sometimes referred to as l-thyroxine or synthetic T4.

Levothyroxine is the most commonly prescribed thyroid hormone replacement medication, used to treat an underactive thyroid, known as hypothyroidism.

There is a great deal of misinformation regarding the safety and effectiveness of generic levothyroxine, versus brand names, which in the US include Synthroid, Levoxyl, Unithroid, and Tirosint (a hypoallergenic, liquid gelcap formulation of levothyroxine.)

Here's the key information you need to know about brand name versus generic levothyroxine.

The Potency Question

A key challenge with generics, and a valid complaint by doctors is that when you have a prescription for generic levothyroxine, every time you get a refill, you may get a levothyroxine made by a different company.

Levothyroxine is required to fall within 5% of its stated potency. Each company's formulas tend to be consistent, so if drugmaker A's product is usually 96%, it will be consistently so from refill to refill. But drugmaker B's products may typically run at 105% of potency.

So, using the example of a 100 mcg levothyroxine tablet, Drugmaker A's 100 mcg tablet delivers 96 mcg of active levothyroxine. Drugmaker B's delivers 105 mcg of active levothyroxine. Going from Drugmaker A to B's product would be a difference of around 65 mcg per week - almost like taking an extra pill each week!

(Go from B to A, and it's like dropping a pill each week!)

So, with every refill of a generic levothyroxine, you run the risk of getting a product from a different drug maker, with different potency. This could affect your thyroid replacement, your symptoms, and TSH levels.

This is particularly a concern for thyroid cancer survivors, who require careful and consistent dosing in order to suppress TSH as a way to prevent cancer recurrence.

How to Minimize Potency Fluctuations with Generic Levothyroxine

Doctors say that there is nothing wrong with generic levothyroxine drugs. They are as safe and effective as the brand names. But if you are going to take generic levothyroxine, you'll need to figure out how to minimize the effects of any potency fluctuation.

  1. Get a Large Supply: One way to minimize this fluctuation is to get a supply that will last for some time. Consider getting your doctor to write you a prescription for a six-month supply, for example. (Make sure, however, that you get a fresh batch, one that will not expire until long after you will have used up the six-months' worth of drugs.)
  2. Work With Your Pharmacist: If you are stabilized on a generic levothyroxine, find out who the manufacturer is. While your doctor can't prescribe a particular generic manufacturer's levothyroxine, if you have a relationship with your pharmacist, you can ask specifically if they will fill your prescription with the particular generic that works for you. Many pharmacists will work with customers in this way. (Note: This tends to work with smaller pharmacies, but may be difficult with larger drugstores and chain stores, or mail-order pharmacies.)

    If You Have to Take Generic Levothyroxine

    If because of cost, insurance, or your HMO, you are forced to take a generic, and can't guarantee that you are getting refills from the same generic maker, monitor your symptoms carefully after each refill. If you have symptoms, talk to your doctor about having your thyroid levels rechecked to ensure that you are not experiencing potency fluctuations.

    When Generics Don't Work 

    If you have tried generics and have found they don't work as well as a particular brand name of levothyroxine, your physician will need to write your prescription along with the special designation "DAW" or "dispense as written" along with "no generic substitution." This way, you have a better chance of having your insurance company or HMO fill the brand name prescription as written, without attempting to substitute a lower-cost generic.

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