According to the Food and Drug Administration (FDA), nearly 8 in 10 prescriptions filled each year in the United States are for generic drugs. Generic drugs typically cost from 80 to 85 percent less than brand name drugs.
A generic drug is a drug that has the same active ingredients as the brand name drug. To be an FDA-approved generic drug, the drug needs to be tested and proven to contain the same active ingredients, the same dosage form, and the same route of administration (i.e., oral, topical, injection).
After patent protection expires, generic manufacturers must seek FDA approval to produce generic versions of the brand name drug. For most brand name medications, there are several approved generic versions made by different generic drug companies. When you are taking a generic drug, this means that every time you get a refill, you receive whatever medication is in stock at the pharmacy.
Brand name and generic thyroid drugs
Generic drugs are available in many categories of thyroid medications.
- Levothyroxine: Levothyroxine is a thyroid hormone replacement drug used to treat hypothyroidism. The brand names of levothyroxine in the U.S. include Synthroid, Levoxyl, and Tirosint. According to the FDA, there are at least three companies making generic levothyroxine, including Lannett, Mylan, and Merck.
Liothyronine: Liothyronine (synthetic T3) is a thyroid hormone replacement drug used to treat hypothyroidism. The only brand name liothyronine drug in the U.S. is Cytomel. Drugs.com lists at least four generic manufacturers of liothyronine, including Mayne, Mylan, Sigmapharm, and Sun Pharm.
Natural desiccated thyroid (NDT): Natural desiccated thyroid is a thyroid hormone replacement drug for hypothyroidism. The brand names of NDT in the U.S. include Nature-throid, WP Thyroid, and Armour Thyroid. One generic NDT, known as NP Thyroid, is made by Acella.
Methimazole: Methimazole is an antithyroid drug used to treated hyperthyroidism. The only brand name of methimazole in the U.S. is Tapazole. Generic methimazole is available from a number of companies, including Sandoz, Cedar Pharmaceuticals, Activis, Caraco, and Par Pharmaceuticals.
Propylthiouracil (PTU): The antithyroid drug PTU, used to treat hyperthyroidism, is only available as a generic in the U.S.
Thyrotropin alfa: The drug thyrotropin alfa, used as part of monitoring tests in thyroid cancer patients, is currently under patent, and only available under its brand name, Thyrogen.
General challenges with generic drugs
There are several reasons why you may find that you react differently to a generic drug as compared to a brand name.
Variability in potency: The FDA allows for as much as a 4 percent variation in potency, to account for different manufacturing processes. This means that potency can vary when you switch from a brand name to a generic version of a drug, or switch from one generic drug to another. This variation in potency is enough to allow symptoms to resume in some patients.
Different inactive ingredients: While a generic drug has the same active ingredients as a brand name, the FDA states: “Generic drugs do not need to contain the same inactive ingredients as the brand name product.” Inactive ingredients, also known as excipients, have nothing to do with the therapeutic action of the drug. They include dyes, fillers, flavors, and preservatives that are used to produce the pills. They are supposed to be inert, but they can affect how the drug works for you. For example, an allergy or sensitivity to inactive ingredients in one generic versus another, or in a generic versus a brand-name drug, can affect how you respond to a drug.
Differing bioavailability: Generic drugs are considered bioequivalent to the brand name drugs, meaning that they need to have the same therapeutic effect. But they do not have to have the same bioavailability. Bioavailability is a measure of the proportion of a drug that enters your circulation and is able to have the desired effect. The manufacturing process of a generic medication — as well as any ingredients that trigger an allergy or sensitivity — can make one medication less bioavailable to you than another.
The challenge posed by generic thyroid medication
If you are taking a generic thyroid medication, every time you refill your prescription you may receive a product by a different generic drug manufacturer. Again, because of differences in potency and inactive ingredients, you may respond differently to that medication. As a result, you might notice the return of symptoms of hypothyroidism or hyperthyroidism, or changes to your thyroid blood test levels.
In the case of thyroid hormone replacement medication for hypothyroidism, this can be a particular concern. Thyroid hormone replacement drugs — including levothyroxine, liothyronine, and NDT — are categorized as narrow therapeutic index (NTI) drugs. NTI drugs are drugs that treat conditions that require close control and consistency.
This is of greatest importance for thyroid cancer survivors taking suppressive thyroid hormone replacement. The goal of suppressive therapy is to keep your thyroid stimulating hormone (TSH) level low or nearly undetectable to help prevent recurrence of thyroid cancer. Because suppression is so important, experts recommend that thyroid cancer survivors on suppressive therapy remain on a consistent brand-name levothyroxine drug.
Flaws in levothyroxine bioequivalence
According to the American Thyroid Association (ATA), despite the FDA’s assertions, you can’t be truly confident in the bioequivalence of levothyroxine. They have stated:
“Most endocrinologists believe that the FDA’s methods for testing the equivalence of thyroxine preparations are seriously flawed. One of the problems with the FDA’s methods is that they do not use TSH blood tests, the cornerstone of thyroxine monitoring, to compare different thyroxine preparations in study participants. Another concern is the many factors that can influence thyroxine absorption and availability to your body. There is variation in the thyroxine content among the various approved preparations with the same stated dose on the tablet.”
As a result, the ATA recommends that whenever possible, patients remain on a brand name levothyroxine drug.
Recommendations regarding your thyroid medication
Your medication is an important part of treating your thyroid condition. Here are some important recommendations:
- Your brand (or generic manufacturer) of thyroid drugs should be constant.
- Don’t allow your pharmacy to substitute a generic for a brand name, or one brand for another. Check labels and the pills themselves every time you get a refill.
- If your insurance company, health maintenance organization , or state aid program will not cover the cost of a brand-name drug, or charges a higher copayment, ask your doctor to write the prescription as "no substitutions, dispense as written (DAW)."
- If you need to stay on a brand name, but it is not covered or requires a higher copayment, ask the pharmacist what the retail cost is if you purchase it directly. In some cases, the retail cost is affordable, and may even be less than your required copayment.
- If you must switch from one brand to another, or from a brand name to a generic, you should be retested within 8 to 12 weeks to ensure that you don’t need a dosage adjustment.
Taking generic thyroid medications
If you need to take a generic thyroid medication, there are two ways to help minimize any negative impact on your health.
1. Get a longer-term supply of your medication. If you can get a medication supply that lasts three to six months from the same manufacturer and batch, this helps to ensure consistency over a longer timeframe.
2. Find a friendly pharmacist: If you have a personal relationship with your pharmacist, he or she may be willing to ensure that you get a generic from the same drug manufacturer with each refill. This can be difficult if you work with a larger, multi-staff pharmacy or chain. But smaller, local pharmacies may be willing to work with you this way.