Levothyroxine is one of the most commonly prescribed medications in New Zealand for managing hypothyroidism. Despite its widespread use, many individuals taking this medication may not fully understand what is inside their levothyroxine tablets and how these ingredients work in the body. If you’re currently on levothyroxine or considering it for thyroid management, it’s essential to know exactly what this medication contains and how it functions.

Disclaimer: If this blog resonates with you or you have concerns about taking levothyroxine, please speak with your GP for further guidance and support.

What’s in Levothyroxine?

Levothyroxine contains two key types of ingredients: active ingredients and inactive ingredients. Understanding both can help you make informed decisions about your treatment and its effectiveness.

Active Ingredients

The active ingredient in levothyroxine is thyroxine (T4), which is a bio-identical form of the thyroid hormone your body would normally produce. When your thyroid is underactive (hypothyroid), it is unable to produce adequate amounts of this hormone. That’s where levothyroxine comes in, supplementing your body with the T4 hormone it’s lacking.

The amount of thyroxine (T4) varies depending on the strength of the levothyroxine tablet you are prescribed. Levothyroxine is available in various doses, typically ranging from 25 mcg (micrograms) to 300 mcg.

The dose you take is based on how much thyroxine your body needs. Most people with hypothyroidism will take a dose between 75 mcg and 125 mcg, as this is the typical amount a healthy thyroid would produce daily. However, factors like genetics, metabolism, and your body’s ability to absorb the medication may influence your required dose.

Inactive Ingredients

Inactive ingredients, although not responsible for the therapeutic effect of the drug, play an essential role in the pill’s composition. These ingredients help support the manufacturing process, stabilize the medication, and sometimes assist in the absorption of the active ingredient. However, for thyroid patients, these ingredients can sometimes cause reactions or sensitivities.

Common inactive ingredients found in levothyroxine tablets include:

• Magnesium stearate – Used as a binder and lubricant to aid in the manufacturing process. It’s generally safe and doesn’t have studies indicating harm.

• Microcrystalline cellulose (MCC) – This is often referred to as wood pulp and helps absorb moisture and aids in the tablet’s disintegration. It’s considered safe for most individuals, though a small percentage may experience mild side effects.

• Colloidal silicon dioxide – An anti-caking agent that allows the powder in the tablet to flow easily during manufacturing. It’s safe in small amounts but should be avoided in powdered form (inhalation can cause respiratory issues).

• Sodium starch glycolate – Known as a "super-disintegrant", it assists in tablet dissolution and enhances absorption. Some people may be sensitive to it, particularly if it’s sourced from rice, corn, or potatoes.

The color additives used to differentiate the various doses are also technically inactive ingredients but can be important for patients who are sensitive to specific dyes. For example:

• 25 mcg tablets: FD&C Yellow No. 6 Aluminum Lake

• 75 mcg tablets: FD&C Blue No. 2 Aluminum Lake, D&C Red No. 27 Aluminum Lake

• 100 mcg tablets: D&C Yellow No. 10 Aluminum Lake, D&C Red Lake Blend

While these inactive ingredients are typically present in small amounts, they can sometimes cause issues for sensitive thyroid patients. If you're concerned about these additives, some people prefer taking the 50 mcg levothyroxine tablets, as they contain fewer color additives.

Additional Considerations About Levothyroxine

Here are a few additional important points to note when taking levothyroxine:

1. Levothyroxine Contains Iodine

It’s important to note that all forms of thyroid medications, including levothyroxine, contain iodine. This is because iodine is naturally found in thyroid hormones, including T4. While the amount of iodine in levothyroxine tablets varies, it is estimated that each dose of levothyroxine provides approximately 40-50% of its mcg dose in iodine.

For example, if you’re taking a 100mcg dose of levothyroxine, you’re also increasing your iodine intake by 40-50 mcg. Since the recommended daily iodine intake for most people ranges between 150 and 300 mcg, it’s something to keep in mind.

2. Synthroid and Levothyroxine Are Not the Same

Many people confuse Synthroid and levothyroxine as being identical, but they are not the same medication. Synthroid is the brand-name version of levothyroxine, and while they both contain the same active ingredient (T4), their inactive ingredients can differ.

For example, Synthroid contains lactose and some other ingredients that are absent in generic levothyroxine. For some patients, this difference can impact how well the medication works for them. It’s worth discussing with your healthcare provider if you experience symptoms that may be related to these inactive ingredients.

3. Levothyroxine May Not Work for Everyone

Though levothyroxine is the most commonly prescribed medication for hypothyroidism, it doesn’t always work for everyone. Some thyroid patients may still experience symptoms even when taking the correct dose. This could be due to a variety of reasons, including how well the body absorbs the medication, how sensitive the patient is to the inactive ingredients, or other underlying conditions.

If you’re not feeling better despite taking your medication, you should speak to your GP. They may suggest trying alternative thyroid medications, adjusting the dose, or investigating other factors impacting your thyroid health.

Alternatives to Levothyroxine

If you find that levothyroxine isn’t providing the relief you need, there are alternatives available. These include:

• Synthroid – A brand-name version of levothyroxine with slightly different inactive ingredients.

• Levoxyl – A gluten-free and lactose-free alternative.

• Tirosint – A gel capsule with fewer inactive ingredients.

• Tirosint-Sol – A liquid form with minimal inactive ingredients, ideal for those with sensitivities.

These alternatives may provide a better solution depending on your specific needs and sensitivities.

Final Thoughts

Levothyroxine is a critical medication for managing hypothyroidism and is usually very effective when taken properly. However, understanding the active and inactive ingredients in your medication can help you avoid unnecessary complications and ensure the medication works for you. If you are concerned about levothyroxine or experience issues despite following your treatment plan, don’t hesitate to reach out to your GP for further guidance.

Disclaimer: If you’re unsure about your medication or have concerns, please consult with your doctor or healthcare provider. They are the best resource for personalized advice and support.