How toxic are cns depressants?

Depends: Alcohol is an example-- depends how much you use and for how many years. Benzos and barbituates are also examples. If you've been using alcohol or these meds multiple times a day for a long time, you don't want to suddenly stop them, as that can cause seizures and other dangerous consequences. Discuss weaning them with your doctor. Alcohol in moderation, and use your meds as prescribed to you!