Dextromethorphan
cough
"One of the most horrible drugs I've taken in my life. Mind you it was very effective at suppressing the cough, but it gave me vertigo like no tomorrow. I had HUUUUGE dilated pupils, severe dizziness, vertigo (cannot walk unassisted), confusion and retrograde amnesia. I had to take one day off work  plus the whole weekend to lay in bed trying to fight the dizziness. It is now the 4th day since I took the drug (extended release pill x 3 doses) and I'm still fighting the side effects. It has severely impaired my ability to concentrate at work and I do not recommend this for ANYBODY."