A reader writes:
The argument against a blood level, since regular users could exceed that level and not be impaired, is very darkly amusing to me. The EXACT same argument could be made regarding alcohol. I'm an emergency physician and toxicologist. I take care of patients who would be in life-threatening alcohol withdrawal at the legal limit blood level of 0.08. I also have had patients walking and talking with levels well over 0.4, and new teenage drinkers who are comatose with a blood alcohol level half that. We use "clinically sober" as a criteria for being safe to discharge a patient, not their blood alcohol level. We need laws to reflect "driving while impaired," for any reason. That would cover users of pain medications, antihistamines, people who are sleep deprived, etc.
My family has plenty of personal and painful experience with being hit by drunk drivers, and I am all for locking people up for that offense. I don't drink at all if I am going to be driving. Period. I think drunk drivers need to go to jail. But it is wrong to think that the degree of impairment can be determined by the blood alcohol level.