it is available at any health food store?

btw, here's an article i found:

Over 4 million Americans this year will suffer from constipation.1 There are many causes of chronic constipation, among them: diet, low levels of physical activity, drugs (OTC and prescription), low potassium levels, pregnancy, diabetes, chronic enema use, and others. Most chronic constipation can be alleviated by simply adding bran or prunes to the diet. Adding 1/2 cup of bran and increasing to 1 1/2 cups over two weeks time should resolve the problem. Eight ounces of prune juice should also do the trick. If you choose to add bran, be sure to consume large amounts of water.

If this doesn't help and you have tried a bulking laxative, cascara sagrada provides a temporary solution. DO NOT USE ANY STIMULATING LAXATIVE FOR MORE THAN 10-14 DAYS! If you have been using stimulating laxatives you may need to retrain your bowels. Here's how:
eat a high fiber diet
drink LOTS of water
sit on the toilet everyday at the same time, regardless of urge or absence of urge to defecate--morning is best
never repress the urge to have a bowel movement
get some exercise every day
for one week take just enough cascara sagrada at night to ensure a bowel movement in the morning
after one week, taper the dose by half each week until it is no longer needed
don't do it again, mister!