Is it possible for medication to harm the egg quality? like xanax? (taken before conception, not after) is there more chance for miscarriage or birth defects when you took it months before conception if it harms the egg quality?

The answer is more broad than you would think. Each medication has its' own safety profile and effect is specific to that med. Egg effect is also a broad issue since a woman caries all her eggs in her ovary from birth, and there may be an effect from a variety of exposures that occur any day of her life. The quality of an egg at release reflects all past exposures.(birth on until release)