Whether you suffer through work with a migraine or call in sick, your work productivity suffers. And when you add up all the lost workplace productivity caused by migraine across the country, it amounts to a huge economic drain, according to two recent studies.

The first, a survey of 500 people, found that more total work hours were lost from presenteeism—reduced work performance on the job—than from absenteeism. The migraineurs, who averaged two to eight attacks per month, missed work for 28% of attacks and stayed at work for 62%. Because their productivity dropped an average of 25% when they stayed on the job, researchers estimated the group lost 1,301 hours from presenteeism and 974 from absenteeism.

The second study compared lost productivity in people with chronic migraine versus those with episodic migraine. Those with the chronic condition (15 or more attacks per month) lost almost four times as much productive time as those with episodic migraine.

“Lost work time–whether by absenteeism or reduced productivity while at work–costs this country more than $20 billion a year in both direct medical expenses and in missed work and lower productivity,” said Walter F. Stewart, MD, PhD, lead author of the study.  “Our purpose was to see how much more chronic migraine costs us than episodic migraine which appears to be substantial.”

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