Taking any drug, including over-the-counter drugs, comes with a certain level of risk. Side-effects can range from upset stomach to severe illness or addiction. The same holds true for medications used to treat bipolar disorder. The benefits usually outweigh the risks, but it’s important for patients to understand and be on the lookout for side-effects of medication. Recognizing the difference between a symptom and a side-effect helps people to communicate with their mental health professionals and medication can be adjusted accordingly. One side-effect of bipolar disorder medications patients might miss is the development of hypothyroidism.
The thyroid is a small, butterfly-shaped gland located in the neck and is primarily controlled by the pituitary gland with thyroid stimulating hormone (TSH). The thyroid then produces hormones that play a major role in growth, muscle strength, menstruation, metabolism and energy regulation. It works by synthesizing iodine found in food into the hormones T3 and T4. These are the hormones that will go on to help control body temperature, heartbeat and how the body breaks down food, among other functions.
Hypothyroidism occurs when the thyroid produces too few hormones. Causes of hypothyroidism include immune disorders, inflammation, radiation treatments and some medications (like those for bipolar disorder). Symptoms include:
- Weight gain
- Intolerance to cold
- Dry skin
- Hair loss
- Brittle nails
- Joint and muscle pain
- Decreased heart rate
- Irregular menstruation
Unfortunately, bipolar disorder symptoms also include fatigue, weight gain, body aches and depression. So, hypothyroidism, especially subclinical, can be easily overlooked in people with bipolar disorder.
Previous research has demonstrated that thyroid disease is more common in people with mood disorders, especially rapid-cycling bipolar disorder, than in the general population. However, it is possible for people to develop hypothyroidism because of the medication they’re taking.
The connection between lithium and hypothyroidism is well-known among researchers. It inhibits iodine uptake in the thyroid. Without iodine, the thyroid can’t produce the hormones required to function normally. Because of this, practitioners generally have a patient’s thyroid function tested both prior to starting lithium treatment as well as periodically during treatment. In some cases, lithium-induced hypothyroidism becomes permanent.
New research published in the journal Bipolar Disorders indicates that lithium may not be the only culprit in bipolar disorder treatment-induced hypothyroidism. It may not even be significantly more risky than other common treatments.
Researchers studied the medical records of more than 24,000 people to find the correlation of developing hypothyroidism after beginning treatment. They examined the rates of nine common medications used to treat bipolar disorder.
When looking at the risk of developing hypothyroidism over four years of treatment, researchers found that 8.78% of people taking lithium developed hypothyroidism. The percentage of patients with who developed hypothyroidism after beginning the other eight medications are:
- Quetiapine (brand name Seroquel): 8.26%
- Lamotrigine (Lamictal): 7.06%
- Valproate (Depakote): 7.02%
- Aripiprazole (Abilify): 6.99%
- Carbamazepine (Tegretol): 6.73%
- Risperidone (Risperdal): 6.46%
- Olanzapine (Zyprexa): 6.43%
- Oxcarbazepine (Trileptal): 6.32%
So, while lithium remained the top culprit, quetiapine is an incredibly close second, and the least likely is still within 3%. This is significant because only 40% of patients taking medication for bipolar disorder have their thyroid function tested before or during treatment. Those taking lithium are twice as likely to be tested as those taking any other medications.
It is possible that the development of hypothyroidism is not directly caused by these medications. Some research has indicated that those with low-functioning thyroid have a greater risk of developing bipolar disorder and vice versa. Regardless of the cause, it’s important for healthcare professionals to regularly test the thyroid function of patients with bipolar disorder.
Hypothyroidism is easily treated with medications like levothyroxine (Synthroid), and doing so helps reduce the negative effects of hypothyroidism on bipolar disorder.
Image credit: Yoan Carle