This is an exerpt from 10 ESSENTIAL HERBS by LALITHA THOMAS (my bible...I love this book!).

Ginger taken internally, either as a powder or as fresh Ginger root tea, acts as a stimulant to the digestion and to the action of the intestines. This is how it gets the bowels moving without being a harsh purgative. A natural "side effect" of drinking Ginger tea regularly is that often the intestines evaucate much more efficiently. For the worst constipation, a Ginger tea enema will immediately clear the large intesting while at the same time stimulating peristalsis, relieving gas, and increasing circulation to intestinal tissues. (NOTE: I tried it. It's very powerful). While you should avoid the use of enemas and/or laxatives for the elimination of body wast, a Ginger enema, when called for, is an invaluable measure to know about. In the most sever cases you can both do the enema and take the Ginger orally for constipation relief. Often, however, simply taking a generous dose of Ginger powder (1 Tbsp) two or three times during the day with a full glass of water will get the results needed.
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Cayenne pepper is also very useful for constipation. Lalitha Thomas writes:
Because Cayenne can stimulate digestive action in the intestines (peristalsis), one can often help relieve constipation by using Cayenne either regularly or just when an occasional need arises. This is a good remedy to know when you are traveling.
Dosage: 1/2 tsp in 1 cup of warm water as needed.

(I have had good results placing the dose in the center of my tongue and washing it down with juice--it reduces the burn!)