Teeth grinding can be caused not just by stress and anxiety but by sleep disorders, an abnormal bite or teeth that are missing or crooked.
Many of the treatments for teeth grinding, also known as bruxism, do not include medications. Your dentist can fit you with a mouth guard to protect your teeth while you sleep.
If stress is the cause you need to find a way to relax. Meditation, counseling and exercise can all help reduce stress and anxiety.