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Low Thyroid Levels Impair Driving as Much as Alcohol Intoxication

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An underactive thyroid gland can cause fatigue, weakness, constipation, dry skin and depression. New research now shows that it can also have a negative impact on driving safety.

When thyroid hormone levels drop, the consequences can include clumsiness as well as cognitive difficulties, but most people don't realize how serious this can be. Researchers at the University of Kentucky tested 32 people with thyroid cancer who had to stop taking thyroid hormone for medical tests. They were given several psychological tests and asked to perform in a driving simulator. Later, after they had again started taking thyroid hormone, they were retested.

The scientists found that low thyroid hormone levels increased braking time, presumably because reflexes were slowed. The impairment was comparable to that seen with alcohol intoxication. Once the levels were normalized, driving ability improved.

[International Society of Endocrinology, June 21, 2014]


The People's Pharmacy perspective finds this research both fascinating and scary. It is not uncommon for visitors to our site to report that it took many months before their health problems were diagnosed as an underfunctioning thyroid gland. During all that time, they were probably not performing at their best in many areas of their lives, including behind the wheel. Which of the drivers on the road with you is suffering with inadequate thyroid hormone? How is your thyroid doing?

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Before I was diagnosed with an underactive thyroid, I experienced two scary incidents involving failure to brake appropriately when approaching stopped vehicles (luckily I did not impact either vehicle, but I scared everyone around me), and one incident of falling asleep while driving.

In that incident, I think the drivers behind me recognized something was wrong, and gave me room to recover without incident to myself or other cars. I reported these to my doctor, who was sharp enough to order TSH and B-12 tests, both of which indicated I needed additional supplements. I have not had repeated occurences of these incidents in the 8 years since I began treatments.

I was diagnosed with hypthyroidism many years ago. I take synthroid everyday before breakfast. I have been driving for over twenty years. Even though my condition is under control with my medication-- there are times when I am driving I feel fuzzy and about to lose control of my truck. I thought there was something wrong with me, but now that I have read your article; it all finally makes sense. I encourage anyone who experiences fuzziness when driving to get their thyroid level checked.

Thanks.

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