Two herbalists for whom I have much respect, discuss the use of poke root for certain ailments. It is something I would consider using with great caution and care.
I can give you a recipe for Poke Root Tincture, but it takes six weeks to make and if you have mastitis now, that would take too long. Plus you need to harvest the root in the fall....
I do not know of a reputable source for Poke Root tincture. Likely because it can be dangerous, companies are not willing to sell it. Because it is such a strong remedy and potentially dangerous, I would not get it from a source unless I was very confident about it.
The author of this post is suggesting taking it internally and using it topically for mastitis. If using it topically, you would still use a tiny amount and make sure the baby would not get any at all, even in a tiny quantity. One drop of poke root tincture is the internal dose, so it is very, very strong.
If I were to have poke root tincture in my house, it would be in a very safe place. Most herbal/natural things that I use are so safe I can leave them accessible. Not so with poke! An over dose could be very serious or fatal. And when a beginning dose is one drop...well, you see what I mean.
I have a great respect for poke and it is something I would consider using for a serious condition.
For mastitis, I would try something else first. I have had much success with many different mastitis remedies over the years. (I nursed 9 babies for a year or more each and have had my share of mastitis! )
Warm compresses, peppermint essential oil, mullein/lobelia salve, cabbage poultices, charcoal poultices....
~Mama to Many~