jdunk is right. Care should be taken!

In my case it was because I was on an anti-seizure med at the time.
Be alert that the combo can cause serious actions/reactions. It should be outlined in that teeny, fine-print brochure you get w/your meds called drug/prescribing information. Look it up on the web? You can actually enlarge it to READ IT!
Also know that the ‘alternatives’ often take a few more minutes to kick in and also wear off faster. So make sure you and your dentist are clear on hand signals or certain sounds that you mite make to indicate distress or OW!
Hope this helps?