What Happens If I Take Too Much Thyroid Medicine?

Your thyroid is a small gland nestled just under your skin in the front of your neck. It controls hormones that affect the way your body uses energy. An imbalance of these hormones may be helped by taking certain medicines. Missing a dose of thyroid medicine or doubling a dose may have different effects than other types of medication. Give the Missouri Poison Center a call if you double-dose or accidentally take more than you need.

What are the main hormones that the thyroid affects?

There are two main types of thyroid hormones: T3 or triiodothyronine and T4 or thyroxine. T4 is inactive; the body converts it into T3, the active form. They go hand-in-hand and are usually referred to together as just your “thyroid hormone.” T3 and T4 affect your metabolism, or the way your body transforms the food you eat into energy. 

The amount of thyroid medicine someone needs to take to balance their system depends on many factors, like age, medical history, and more. Sometimes, someone may not be able to convert T4 into T3, which affects their treatment plan. 

What foods and supplements affect thyroid medicine absorption?

Thyroid medicine may be affected by the things you eat around the time you take your medications. It’s best to take thyroid medicine on an empty stomach and to avoid anything that interacts with absorption for a few hours before and after.

Food and supplements that may affect medicine absorption include:

• Iron supplements
• Calcium supplements and calcium-fortified products, like some juices and dairy
• Antacids
• High-fiber foods
• Walnuts
• Soy and soy-fortified products
• Coffee

It’s important to alert your healthcare provider if you change your diet from high- to low-fiber, as this will affect your hormone levels. Also, let them know about any supplement changes you’ve had, as well as any “natural, thyroid-energizing” or “supporting” supplements you try.

What if I accidentally take two thyroid pills?

As a rule of thumb, do not double up if you miss a day for most medications, specifically thyroid medicine. This is because thyroid medicine stays in the body for a few days and takes time to be broken down and used by the body— it won’t make up for the lost day. The level of the thyroid hormone in your body is meant to be in a specific range, and taking two doses at once may increase the risk for unwanted side effects or cause toxicity. 

If you took two thyroid pills by accident or doubled up after missing a dose, there is no need to panic. Doubling up once is unlikely to cause serious harm for most people. Don’t induce vomiting (more on why this isn’t helpful in this blog article here). Instead, contact your healthcare provider or the Missouri Poison Center and monitor for symptoms like rapid heartbeat, tremors, anxiousness, flushing, and increased temperature over the next few days. 

Hyperthyroidism vs Hypothyroidism

Both of these medical terms deal with an imbalance in the body’s ability to regulate thyroid hormones. Hypothyroidism occurs when the body does not make enough of the hormone (underactive). Hyperthyroidism occurs when the body makes too much (overactive). 

Not all of the body’s hormones are alike. Some are fast-acting, like adrenaline, which takes effect within seconds. Others take weeks or more to manifest; thyroid hormones fall under this slow-acting category. Beginning treatment for either hyper- or hypothyroidism may take 4-6 weeks before symptoms are relieved. Therefore, the key is consistent dosing and patience.

Hyperthyroidism

An overactive thyroid will make too much thyroid hormone, speeding up your metabolism. This may cause symptoms such as weight loss, anxiety & restlessness, fast heart rate, sensitivity to heat, and insomnia.

Medications for hyperthyroidism work to block hormone production. These are called antithyroid medications; the main ones are methimazole (Tapazole®) and propylthiouracil (PTU). 

Other options for treating hyperthyroidism include surgery or taking radioactive iodine, which prevents the thyroid from working ever again. Someone who opts for either treatment would need to take thyroid hormone medicine for the rest of their life, as they would otherwise suffer from hypothyroidism.

Hypothyroidism

This is when the thyroid is underactive, meaning the body’s metabolism is slower than normal. The body cannot use the energy it has available, leading to symptoms like lethargy, weight gain, hair loss, cold sensitivity, and fatigue.

Replacing the body’s thyroid hormone is the most common treatment. Levothyroxine is a type of synthetic T4 prescription you might get; liothyronine is a synthetic version of T3. There’s also a type of medication called natural desiccated thyroid, or NDT. This type comes from a pig’s thyroid gland. 

What are the side effects of too much thyroid medication?

It’s important to work with a healthcare provider to find the right dose of thyroid medicine for you. 

Taking too much levothyroxine for hypothyroidism may result in symptoms of an overactive thyroid. Here are a few signs your thyroid medication may be too high:

• Irritability or nervousness
• Tremors
• Vomiting
• Diarrhea
• Heart palpitations
• High blood pressure
• Increased sweating
• Unexplained weight loss

Taking too much antithyroid medication for hyperthyroidism may result in symptoms of an underactive thyroid, such as:

• Loss of energy
• Dry skin
• Hair loss
• Muscle aches and joint pain
• Cold sensitivity
• Unexplained weight gain
  

In either case, be sure to reach out to your healthcare provider to test your thyroid hormone levels and adjust your medicine dose accordingly. Results from adjusting the dose may not be seen for at least a few days.

Can you overdose on thyroid meds?

Accidentally taking one extra dose of thyroid medication is unlikely to lead to significant overdose.

That being said, it is possible to overdose on thyroid medicine by chronically misusing it (at a dose much higher than prescribed) or accidentally swallowing quite a few doses. 

Overdose symptoms may be delayed for hours or days before they appear. 

Contact the Missouri Poison Center with questions or for help with an exposure at 1-800-222-1222.

Tips for Preventing Missing Future Doses

Do you keep missing doses of your thyroid medicine? Here are a few tips to help you stay consistent:

• Take medicine at the same time as you do another daily task, like brushing your teeth. Since levothyroxine needs to be taken on an empty stomach, try making it the first thing you do in the morning.
• If refilling a weekly pill organizer is a problem, try using multiple or large organizers that give you more time between refills. Keeping an organizer helps you know if you’ve already taken your daily dose. These are helpful, but young children find them easy to open. Store pill organizers out of sight and reach of children.
• Set an alarm or reminder on your phone. There are apps that have games or rewards built in to reward a person for following their dosing plan. 
• Try asking a friend or loved one to check in with you about taking daily medications until you’ve built a consistent habit.

Final Thoughts

The amount of thyroid medicine you are prescribed is between you and your healthcare provider. Everyone misses a day from time to time; in any situation, the most important thing to do is stay calm and contact the right resource for help. The Missouri Poison Center is open all day, every day, to take your calls about anything poison-related. It’s always free, and always confidential.