Is Synthroid Better Than Generic Levothyroxine?

Comparative Safety of Synthroid and Generics

FDA-licensed generic levothyroxine products are as safe as Synthroid, with no evidence indicating any are “more safe” or “less safe.”

Safety is partly assured by certification from the United States Pharmacopeia (USP), which verifies that the drug contains the correct amount of listed ingredients and is free from impurities.

All generic levothyroxine products in the U.S. have this independent certification.

While some people may be sensitive to inactive ingredients like lactose or color additives, these are usually present in small amounts that pose minimal health risks.

Risk of Heart Disease?

Earlier studies suggested that generic levothyroxine might increase cardiovascular disease risk compared to Synthroid.

People with hypothyroidism generally have a higher risk of heart attacks, heart failure, atrial fibrillation, and stroke. However, managing thyroid levels with levothyroxine can significantly reduce these risks.

Concerns about generic levothyroxine’s effectiveness were largely alleviated by 2019 research published in the Mayo Clinic Proceedings. This analysis of more than 87,000 patients found no difference in the rates of heart attack, heart failure, atrial fibrillation, or stroke between those taking Synthroid and those using generic levothyroxine.

According to the American Thyroid Association, primary care providers are more likely to prescribe generic levothyroxine, while specialists like endocrinologists who treat diseases like hypothyroidism are more likely to prescribe Synthroid.

Cost Difference With Generic Levothyroxine

Generic drugs generally, but not always, cost less than their brand-name counterparts. The longer that a generic drug is on the market, the smaller the cost difference will be (due largely to the decreasing price of the brand-name drug).

With Synthroid, the issue is slightly different. While the drug has been around since 1955, it was only formally approved by the FDA as a “new drug” in 2002. Thereafter, the first generic was awarded FDA approval only two years later, in 2004.

As of 2023, the average retail price of Synthroid 50 mg hovers at around $150 for a 90-day (three-month) supply. In contrast, the average retail price of generic levothyroxine 50 mg is closer to $45 for a 90-day supply.

Effectiveness of Generic Levothyroxine

Prior to the acquisition of Synthroid by AbbVie (then Abbott Pharmaceuticals) in 2001, the FDA received numerous complaints from consumers and medical associations citing inconsistencies in drug quality by the original manufacturer, Knoll Pharmaceuticals.

With the rapid approval of several levothyroxine generics in 2004, these concerns spilled over with organizations like the American Association of Clinical Endocrinologists (AACE) and the American Thyroid Association (ATA) arguing that the newer generics were not bioequivalent to Synthroid.

These authorities argued that FDA policy allows potency ranges of generical to vary by 5%, meaning that the potency can fall anywhere from 95% and 105% of the brand-name product. With levothyroxine, either extreme can be problematic—making it harder to stabilize thyroid function if patients are underdosed with one generic and overdosed with another.

The problem, the AACE and ATA state, becomes even greater if a patient switches between generics or between a generic and Synthroid.

Recent studies have largely allayed some of these fears:

• Differences in efficacy: A 2020 study published in the Journal of the American Medical Association Open Network found that generic levothyroxine is as effective as Synthroid for the initial treatment of mild hypothyroidism. The analysis involved 17,598 adults prescribed levothyroxine from 2008 to 2017.
• Switching between generics: A 2022 study in the Journal of the American Medical Association Internal Medicine found that switching from one generic levothyroxine product to another does not significantly affect thyroid hormone levels in people with hypothyroidism. A total of 15,829 adults were involved in this research.

Can I Switch From Synthroid?

Not all of the concerns about generic levothyroxine have been allayed. For example, if you are taking Synthroid and thinking about switching to save costs, there is evidence that doing so may not be the best idea.

A 2019 study published in Advances in Therapy compared 9,925 adults who consistently used Synthroid to 9,925 adults who switched from Synthroid to a generic. What the researchers found was that people who switched were 15% more likely to have their thyroid hormones fall out of the “normal” range than those who stuck with Synthroid.

While this may suggest that Synthroid is somehow “better” than the generics, there are other possible explanations for the disparity. Among them, studies have shown that the very practice of switching is linked to poor drug adherence. By contrast, sticking with the same drug—irrespective of the drug type—is associated with better adherence and better outcomes.

What You Can Do

Despite some continuing debate over the efficacy of generic levothyroxine vs. Synthroid, most experts agree that the main focus should be placed on taking your thyroid medications consistently and correctly.

To do this:

• Take levothyroxine on an empty stomach 30 to 60 minutes before breakfast to avoid erratic absorption.
• Take levothyroxine at the same time in the morning, keeping to a consistent routine.
• Never run out of drugs. Set a reminder on your cell phone so that you know when to renew your prescription or request a new prescription
• Ask your pharmacist to order the same drug every month. Your healthcare provider can write “DAW” (dispense as written) on the prescription to ensure the same brand is prescribed.
• If you experience an upset stomach or other digestive side effects that make it hard to adhere to treatment, ask about a softgel form of levothyroxine called Tirosint that is more tolerable for people with sensitive stomachs.
• If you are unable to maintain normal thyroid hormone levels despite perfect adherence—ask your provider if you should also take Cytomel (liothyronine), a synthetic version of the thyroid hormone triiodothyronine (T3)—to bolster your response.