The Truth about Generic Prescription Medications with a focus on Thyroid

We are all trying to stick with what is affordable and living paycheck to paycheck.  Health insurance rates are sky high and continue to increase each year.  Some cannot even afford health insurance and are left going to urgent care facilities and emergency departments for health conditions that should be managed and monitored by a family physician.  The goal is to manage your condition effectively, so as to not end up in the emergency room except for a true emergency.

To afford health care and medications often means trying out generic medications rather than name brand.  With some medications, this is going to be just fine, but with some health conditions, it comes at a greater cost to your health and your pocketbook when your condition does not improve and you continue to return to the doctor.

According to the U.S. Food and Drug Administration (FDA):

Today, nearly 8 in 10 prescriptions filled in the United States are for generic drugs. The use of generic drugs is expected to grow over the next few years as a number of popular drugs come off patent through 2015.”

  • When a generic drug product is approved, it has met rigorous standards established by the FDA with respect to identity, strength, quality, purity, and potency. However, some variability can and does occur during manufacturing, for both brand name and generic drugs. When a drug, generic or brand name, is mass-produced, very small variations in purity, size, strength, and other parameters are permitted. FDA limits how much variability is acceptable.
  • Generic drugs are required to have the same active ingredient, strength, dosage form, and route of administration as the brand name product. Generic drugs do not need to contain the same inactive ingredients as the brand name product.
  • The generic drug manufacturer must prove its drug is the same as (bioequivalent) the brand name drug. For example, after the patient takes the generic drug, the amount of drug in the bloodstream is measured.  If the levels of the drug in the bloodstream are the same as the levels found when the brand name product is used, the generic drug will work the same.
  • Through review of bioequivalence data, FDA ensures that the generic product performs the same as its respective brand name product. This standard applies to all generic drugs, whether immediate or controlled release.
  • All generic manufacturing, packaging, and testing sites must pass the same quality standards as those of brand name drugs, and the generic products must meet the same exacting specifications as any brand name product. In fact, many generic drugs are made in the same manufacturing plants as brand name drug products.

Let’s pick some of this verbiage apart now and begin to comprehend it.

Physicians and pharmacists tell us that generic vs. name brand does not make a difference because of the bulleted items posted above.  The reasons are due to the definitions of three fancy terms they assume we know nothing about – bioequivalence, therapeutic equivalence and bioavailability. 

  • Bioequivalence means that two drugs given to the same patient in the same dosage regimen will result in equivalent concentrations of the drug in plasma and tissues.  Generic drugs are required to be bioequivalent to the original brand name drug.
  • Therapeutic equivalence means that two drugs given to the same patient in the same dosage regimen will have the same therapeutic and adverse effects.  Bioequivalent medications are expected to be therapeutically equivalent; however, sometimes they are not.  Often this is only discovered after long-term treatment when patients who have done well on one formulation are switched to another.
  • Bioavailability is the rate at which a drug is absorbed or becomes available to the body at its site of action.  This is where the differences can occur.  Current regulations permit the bioavailability of a generic drug to be plus or minus 20% of the original brand name drug.

Summing it up!


A 20% difference in bioavailability may or may not be significant.  This depends on the medication and the patient’s health condition!  For drugs that have a wide index of tolerance, 20% may not be particularly significant; however, for drugs that have a very narrow therapeutic band, it can make a huge difference.  Moreover, what if a patient taking a generic medication that is plus 20% bioavailability is switched to another generic of the same drug that happens to be minus 20% bioavailability?  That is a huge difference mathematically, and I would think it could make a noticeable difference therapeutically as well.

You must weigh your options and see what works best for your body.  If you feel relief with a generic medication, that is great.  However, if you feel your condition has not improved much or is not being managed well, you should consider asking your doctor for samples of the name brand.  They should have these available, especially for commonly prescribed medications.  Don’t let them fool you, and don’t be afraid to speak up!  I suggest any time you start a new medication, giving it one to three months for your body to fully adjust and make the determination of whether it is helping or not.  Also, have regular labs if the medication is for treatment of a “measurable” condition, for example thyroid disease.


Managing thyroid disease effectively is one of the conditions that the 20% plus or minus can make a huge impact on how you feel.

Synthroid is the most commonly prescribed name brand medication for thyroid disease.  Levothyroxine is the most commonly prescribed generic.

What is important to understand with thyroid disease is that one patient’s “normal” may be completely different from the next patient!  There are many factors that come into play to manage thyroid disease effectively, including knowing your T-3 and T-4 in addition to the TSH (Thyroid Stimulating Hormone).  Many doctors only check the TSH levels and do not pay enough attention to the T-3 and T-4.

Basic Terminology:

T-3 is Triiodothyronine, a thyroid hormone. It plays an important role in the body’s control of metabolism.

T-4 is Thyroxine, the main hormone produced by the thyroid gland.

TSH is produced by the pituitary gland. It tells the thyroid gland to make and release thyroid hormones into the blood.

TSH Normal values range from 0.4 – 4.0 milli-international units per liter (mIU/L). Normal value ranges can vary between labs and even physicians.

If you are being treated for a thyroid disorder, your TSH level will likely be kept between 0.5 and 4.0 mIU/L, except in these situations:

  • For a pituitary disorder, a low TSH may be appropriate.
  • For thyroid cancer, a low TSH may be appropriate to prevent the thyroid cancer from coming back.
  • The normal range for TSH is different for women who are pregnant. Your doctor may suggest that you take thyroid hormone, even if your TSH is in the normal range.

TSH values can vary during the day.  It is best to have levels checked early in the morning.

Again, what is so important to understand here is that while I feel best with my TSH around .98, you may feel your best at a level of 3.0.  There are numerous factors that make this number vary for every individual including other health conditions, other medications you take that may interfere with the absorption of your thyroid medication, and even diet.

You should have your labs checked more frequently if you feel sluggish, notice a change in your tolerance for exercise, have difficulty concentrating,  always feel cold, have brittle nails and hair, and have/are having difficulties with fertility.  Get copies of your own lab work and compare them every 60-90 days for several months to become familiar with your baseline.  If you do not feel right, remember that nobody knows your body better than you! Do not accept your doctor telling you, “it’s in range, so you’re fine!” if you’re having the aforementioned symptoms.  Also, remember that family physicians are general practitioners.  They do not usually have a specialty and therefore refer patients out to specialists.  Do not hesitate to request a referral to an endocrinologist, who can do much more in depth testing and sonograms of your thyroid gland to better determine what is going on and what course of treatment is best for YOU.

thyroid funny


U.S. Food and Drug Administration (

Health Central

U.S. National Library of Medicine