Everyone is too scared to list a dosage, because every one has a different tolerance to it.
That being said, I've swallowed up to 3 frozen berries whole with no issues. It's assumed 10 or more berries will cause gastrointestinal distress.
For purgative effects 1 gram dried root will do. It can be used through a tea, tincture and eaten to get the same effects.
As for the seeds, they are what's use as a poltice to treat external parasites and it would require playing with the dosage to see what you could tolerate. This is pretty much the same for all parts of the plant.