After a cold medicine or an anti-allergy medicine that contains chlorphenamine (also called chlorpheniramine) or diphenhydramine, do not drive while you are taking it, and do not work at a height or operate a machine

Many combination cold medicines mix in an anti-allergy ingredient such as chlorphenamine or diphenhydramine, and taking it makes you drowsy. The national drug regulator says that while you are taking this kind of drug, do not drive, do not work at a height, and do not operate a machine. On a driving simulator, people who had taken diphenhydramine drove worse than people who had drunk alcohol. Feeling that you are not drowsy does not mean the driving is fine.

Cost

No money. Glance at the ingredient list when you buy the medicine. On the days you take it, ride with someone else or take a taxi, or ask a doctor or a pharmacist to switch you to a medicine that does not make you drowsy.

Benefit

A 2010 adverse-reaction bulletin from the National Medical Products Administration says that vitamin C Yinqiao tablets (维C银翘片) contain chlorphenamine maleate, also called chlorpheniramine (扑尔敏). The adverse reactions are mainly drowsiness, a feeling of weakness, sleepiness, and a dry mouth. The bulletin advises doctors and pharmacies to tell the patient: while taking the drug, do not operate an aircraft, a vehicle, or a boat, and do not do work at a height, mechanical work, or operate a precision instrument. A 2020 public medication notice from the National Medical Products Administration says that combination cold medicines often contain an anti-allergy ingredient such as chlorphenamine or diphenhydramine, and that taking them causes drowsiness. People who drive, operate machinery, or work at a height should be cautious. A US driving-simulator trial enrolled 40 drivers with seasonal allergic rhinitis, aged 25 to 44. Each person switched treatment a week apart and drove for 1 hour under each: diphenhydramine 50 mg, fexofenadine 60 mg, alcohol up to a blood alcohol concentration of about 0.1%, and a placebo. Fexofenadine is an anti-allergy drug that does not cause drowsiness. The ability to match the speed of the car ahead was worst after diphenhydramine, and clearly better both after alcohol and after fexofenadine. The ability to hold the lane got worse both after alcohol and after diphenhydramine. When the car ahead suddenly blocked the way, the reaction was slowest after alcohol, a mean of 2.21 seconds, and after fexofenadine it was 1.95 seconds. Driving on fexofenadine was about the same as driving on placebo. The authors' conclusion is that diphenhydramine affects driving more than alcohol does. The drowsiness a driver reported did not show how well they drove, so "whether I feel drowsy" cannot decide whether they can drive.

Notes

The products the drug regulator named, paracetamol with pseudoephedrine, dextromethorphan, and chlorphenamine (酚麻美敏), compound paracetamol and amantadine (复方氨酚烷胺), and paracetamol with caffeine and chlorphenamine (氨咖黄敏), all contain chlorphenamine. Read the ingredient list before you buy. What the Road Traffic Safety Law expressly forbids is driving after a state-controlled psychotropic drug or a narcotic drug. Ordinary cold medicines and anti-allergy medicines are not in that ban. The instruction not to drive is written in the leaflet and in the drug regulator's notice. If you have to take the medicine and you also have to drive, ask a doctor or a pharmacist for a drug that does not make you drowsy. Many of these cold medicines also contain acetaminophen. See item 1 of this section (acetaminophen). Other risks of driving while drowsy are in section 1, item 9 (when you are drowsy, pull over and rest). The grade is B because there is only a single simulator trial of 40 people, and no crash figures from real roads. The benefit is rated small: the endpoint is driving performance in a simulator, not crashes and deaths. Besides you, the people who benefit are family in the car and other people on the road.

Sources · 4

1. 国家食品药品监督管理局 (2010). 药品不良反应信息通报（第32期）关注中西药复方制剂维C银翘片的安全性问题. nmpa.gov.cn/xxgk/yjjsh/ypblfytb/2010091916260…
2. 国家药品监督管理局 (2020). 2020年公众十大用药提示丨（三）感冒用药须谨慎，安全合理是关键. nmpa.gov.cn/xxgk/kpzhsh/kpzhshyp/202011110952…
3. Weiler JM, Bloomfield JR, Woodworth GG, et al. (2000). Effects of fexofenadine, diphenhydramine, and alcohol on driving performance. A randomized, placebo-controlled trial in the Iowa driving simulator. Annals of Internal Medicine, 132(5):354-363. doi.org/10.7326/0003-4819-132-5-200003070-00004
4. 中华人民共和国道路交通安全法（2021 年修正）第二十二条第二款. flk.npc.gov.cn/detail?id=ff8081817ab231eb017a…