Weather and headache onset: a large-scale study of headache medicine purchases.

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It is widely recognized that weather changes can trigger headache onset. Most people who develop headaches choose to self-medicate rather than visit a hospital or clinic. We investigated the association between weather and headache onset using large-sample sales of the headache medicine, loxoprofen. We collected daily sales figures of loxoprofen and over-the-counter drugs over a 1-year period from a drugstore chain in western Shizuoka prefecture, Japan. To adjust for changes in daily sales of loxoprofen due to social environmental factors, we calculated a proportion of loxoprofen daily sales to over-the-counter drug daily sales. At the same time, we obtained weather data for the study region from the website of the Japan Meteorological Agency. We performed linear regression analysis to ascertain the association between weather conditions and the loxoprofen daily sales proportion. We also conducted a separate questionnaire survey at the same drugstores to determine the reason why people purchased loxoprofen. Over the study period, we surveyed the sale of hundreds of thousands of loxoprofen tablets. Most people purchased loxoprofen because they had a headache. We found that the sales proportion of loxoprofen increased when average barometric pressure decreased, and that precipitation, average humidity, and minimum humidity increased on loxoprofen purchase days compared to the previous day of purchases. This study, performed using a large dataset that was easy-to-collect and representative of the general population, revealed that sales of loxoprofen, which can represent the onset and aggravation of headache, significantly increased with worsening weather conditions.