All this talk about what level of impairment is caused by what, is a major problem. Any level of impairment for any reason is a big problem if you are driving. It does not matter what the source of the impairment is. If the sweet old lady that is impaired because of medication that she is taking , runs over me , I am just as dead as if the town drunk hits me. Same for the idiots that text, play with their baby, etc, etc.  When you drive you have an obligation to be capable of doing so in a way that doesn't endanger others. If you don't do that then you should not be allowed to drive. When you are driving, that is not the time to socialize, do business deals, dress, eat lunch or anything other than drive.