Does a glass of wine when taking tegretol stop it from working?

Drinking alcohol can increase some of the side effects of carbamazepine, and can also increase your risk of seizures. Don't drink alcohol.

If carbamazepine is within a therapeutic blood level range, one glass of wine will not alter a pre-existing successful therapy. But as mentioned, side effects from both such as drowsiness or dizziness will be additive, and therefore, not wise to drive when the two are mixed.