The thyroid is a small, sensitive, butterfly-shaped gland located at the base of your neck just above your collarbone. Thyroid disease—especially underactive thyroid, or hypothyroidism—is pretty common. Nearly 5 out of every 100 people ages 12 and older living in the United States have an underactive thyroid, according to the National Institute of Diabetes, Digestive, and Kidney Diseases.
Doctors often prescribe levothyroxine (also sold under brand names such as Levothyroid, Synthroid, Levoxyl, and many others) to treat an underactive thyroid. In fact, levothyroxine is the most frequently prescribed drug in 2019 so far, according to ClinCalc. But getting the dose just right can be a challenge. Here’s why.
The thyroid is a tiny gland that is very sensitive to changes in its environment and stress. This means it is very receptive to levothyroxine and any dose adjustments that might occur.
The catch here is that, despite its sensitivity, it usually takes some time before you and your doctor can see how your body is responding to levothyroxine—regardless of whether you are new to the medication or are taking a new dosage amount
Finding the levothyroxine dose that’s right for you is kind of like trying to balance yourself with a partner on a see-saw in mid-air.
If you push off the ground too hard, the see-saw will become unbalanced and tip all the way over to the other side. Sure, see-sawing up and down is a lot of fun, but your thyroid gland doesn’t like to bounce around a lot.
Although it is sensitive to small changes in levothyroxine, it responds slowly to new doses, so it takes a while to see results.
So when your doctor is adjusting your dose and adjusts your dose slowly, it’s just like giving yourself a slow, gentle push off the ground to bring the see-saw into balance.
The see-saw moves more slowly before finding its resting place in mid-air.
In fact, when you first start taking levothyroxine or your doctor changes your dose, it usually takes 4 to 6 weeks for the see-saw to reach mid-air. And because everyone’s body is different, it may take your doctor a while to figure out the right dose—or how hard you need to push off the ground—to bring your see-saw, or thyroid, into balance.
If your see-saw partner on the other end is heavier than you, you’ll have to work a little harder to balance. If your partner is lighter, you won’t have to push as hard.
If you have an underactive thyroid and are already taking medication for it, you’re already well aware of how finicky your thyroid gland can be.
If you have recently been diagnosed with hypothyroidism and are new to taking medication for your condition, here are a few signs that your doctor may need to adjust the dose of your thyroid medication.
Symptoms of underactive thyroid
- Lack of energy and sluggishness
- Weak and/or slow pulse
- Hair loss or dry, brittle hair
- Dry skin
- Cold hands and increased sensitivity to cold
- Feeling depressed
- Memory problems
- Joint pain
- Bulging eyes
- Hoarse or lower voice than usual
Again, bear in mind that it usually takes 4-6 weeks for your body to respond to see the medication working. And if you’re 65 or older, it might take a few extra weeks to see a difference.
Symptoms of levothyroxine overdose
In general, the most indicators that your doctor needs to adjust your levothyroxine dose is that you start having signs and symptoms of an overactive thyroid. These include:
- Racing or irregular heartbeat or palpitations
- Increased blood pressure
- Faster pulse
- Heart attack
- Difficulty breathing
- Muscle spasm
- Feeling nervous, anxious, or irritable
- Extreme mood swings
- Weight loss
- Muscle weakness
- Unable to tolerate heat
- Changes in your period such as more frequent or irregular periods
However, there are some signs that your reaction to the levothyroxine may be more serious. Cases of a massive overdose may be life-threatening, so you should seek medical attention right away if you have any of the above signs and symptoms coupled with the following below:
- A blood clot in the brain
Although rare, severe cases of levothyroxine overdose can cause coma. Children who take extremely high doses (~20 mg) may be more prone to having seizures.
Also, some people tolerate their levothyroxine well but react to some of its inactive ingredients because they are allergic to them.
With so many brand levothyroxine products as well as numerous generic manufacturers, it is important to pay attention to your body and how you’re feeling.
Signs of an allergic reaction can be itching, skin rash, hives, nausea, vomiting, diarrhea, joint pain, and swelling under the skin most notably on the face, lips, and eyes (a condition called angioedema).
Levothyroxine may sound like a finicky medication to take, but if you are patient with your body and the drug, your doctor can help you figure out the dose that works best for you.
If you have received your first prescription for levothyroxine or if your doctor has recently changed the dose, the best thing you can do is listen to your body. It’s the best indicator of how well your medication is working.
Frieda Wiley, PharmD
Frieda Wiley PharmD, RPh, is a pharmacist, contract medical writer, and consultant. In addition to her consulting work, she has more than 100 publications to her credit, including Costco Connection, WebMD, Arthritis Today, US News & Report, and AARP. Frieda is a regular contributor to the RxSaver blog.
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