What is Reddit's opinion of Medications & Mothers' Milk 2014: A Manual of Lactational Pharmacology (Medications and Mother's Milk)?
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Keep in mind that there are very few studies done on medical effects and lactation because they're expensive and due to liability, anything that hasn't been expressly tested on human subjects, they're going to put that sticker on.

There's a good book Medications and Mother's Milk http://www.amazon.com/Medications-Mothers-Milk/dp/1939847389/ref=sr_1_1?ie=UTF8&qid=1433514830&sr=8-1&keywords=Medications+and+mother%27s+milk that might help alleviate some anxiety about breastfeeding and various medications. But dang I didn't realize it was that expensive! There might be cheaper editions out there.