Should You Take Generic Levothyroxine?

A look at generic versus brand name levothyroxine

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4) and is the most commonly prescribed thyroid hormone replacement medication in the United States. Levothyroxine is used to treat an underactive thyroid, known as hypothyroidism.

Levothyroxine is sometimes referred to as l-thyroxine, L-T4 or synthetic T4.

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 taking generic versus brand name levothyroxine for your thyroid treatment.

The Potency Question

A key concern about generic levothyroxine, and a valid complaint by doctors is that when you have a prescription for generic levothyroxine, every time you get a refill, you can potentially get a levothyroxine made by a different generic manufacturer. 

Levothyroxine is required by law to fall within 5 percent of its stated potency. Each company's formula for a particular dosage of levothyroxine tends to be consistent, so if drugmaker A's product is usually 96 percent, it will typically consistently run at about 96 percent potency. Similarly, if drugmaker B's levothyroxine at a particular dosage typically runs at 105 percent of potency, that will usually be consistent.

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 eliminating a pill each week!)

Because pharmacies are free to fill generic prescriptions with products from any manufacturer (unlike prescriptions that specify a particular brand name) with every refill of generic levothyroxine, you run the risk of getting a product from a different drug maker, with a different potency. This could affect your thyroid replacement stability, your symptoms, and your thyroid-stimulating hormone (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 proven to be as safe and effective as the brand names. But if you are going to take generic levothyroxine, you'll need to determine how best to minimize the effects of any potency fluctuation.

  1. Get a Large Supply: One way to minimize the risks of potency fluctuations 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 your 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, chain stores, or mail-order pharmacies.)

If You Must Take Generic Levothyroxine

If due to cost, insurance, or your HMO, you are forced to take generic levothyroxine and can't guarantee that you are getting refills from the same generic maker, you should 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 due to different product potency.

A Word from Verywell

If you have tried generics and have found they simply don't work as well for you as a particular brand name of levothyroxine, ask your physician 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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