1.will high doses of tizanidine harm kidneys? if so, why and how? 2. can generic brands of meds not work as well or even not at all? thank you!

More likely liver: Tizanidine more likely will cause damage to your liver due to the metabolism of the drug but its about 60 % excreted through the kidneys, so it's possible that it could cause some damage at very high doses, but it normally damages liver. Ibuprofen is more likely causing kidney issues. Generic brands normally work exactly the same as long as they are from reputable companies. Hope this helps!