Cascara sagrada is buckthorn. It also has anthraquinones.

http://www.itmonline.org/arts/laxatives.htm

While an anthraquinone laxative may give you relief, it is likely to cause a worse problem the next day(rebound constipation). There are also longer term safety concerns with these. Try eating more low carb vegetables, drinking more water, taking in herbs like licorice root, ginger, and dandelion that are mild laxatives, and taking a few spoons of coconut oil a day.
Exercise also helps relieve constipation.