I always thought that senna and cascara sagrada were herbal laxatives. This is from memory from more than 2 years ago when people talked about it all the time. But lately I keep reading that only the senna is a problem, so I put the question on Andreas forum.
It is an interesting answer, since he says you should not use it for more than 8-10 days and certainly not with inflammed bowels.
But the other thing he mentioned is Oxypowder , though it is a cleanse, not a laxative, you can get use to that and you really should improve your diet so you don't need any of these.