The fleas themselves do not suffer from the lufenuron, actually. But it is in their system and they lay eggs that cannot hatch out of their shells. It does not kill adult fleas and was actually sort of a failure in controlling fleas, since it did not kill the adults.
It is a lot easier to take it in capsules. Most research shows that a 170 pound person would take about 7 grams. We have found it cheapest at Shop4LDN.com although I bought it first from owndoc.com . Both are good, but I don't like the attitude of the lady at owndoc :-)