I think it's safe - Yerba Mate and Breastfeeding by: Anonymous
I am breastfeeding currently and limit my caffeine intake to green tea and mate, with the occasional cup of half decaf half regular coffee when I really crave it. If you research mate, you'll find that it has only a little more caffeine than green tea, and it has a lot of vitamins and minerals that help even out the effects of the caffeine so it's not as up and down as the feeling you get after a cup of coffee. I was weary of drinking it as I know caffeine passes through breast milk, but after doing some research and trusting my instincts, I have started drinking it again (I stopped during pregnancy because I am pretty sensitive to caffeine and didn't want anything else contributing to my mood swings.) I try to time drinking it right after I feed her or pump so that by the time she eats again(every 2-3 hours) it will be metabolized and out of my system somewhat. You can always try it for a day and see if it makes her fussy. I hope this helps you make your choice!