Same as the study - 600mg once a day in the AM, of N-acetyl-cysteine. It was clear after a few days that it made a difference, too.

Mind you, I've had a hysterectomy (kept ovaries) and take letrozole daily to manage symptoms along with following a strict gluten-free and isoflavone-free diet. There were other supplements I took pre-surgery that helped a lot for the endo pain (like DIM & Calcium-d-Gluconate), as I'm not able to take exogenous hormones (like progesterone) due to bad side effects.