Most people do not use coffee as a laxative in cases of severe constipation, but when digestive problems are minor, coffee can be very effective. Effectiveness depends on the person, his or her current physical health, and any underlying conditions. For some people, coffee actually has the opposite effect and causes severe constipation. It can also cause dehydration. Coffee therefore has some laxative effects, but when a dependable laxative is needed, it is usually not the best option.
The reason this beverage works as a laxative is because it stimulates peristalsis, which is the name for the contractions that move food through the digestive system. Speeding up this process by using coffee as a laxative can cause loose bowel movements, which can be uncomfortable. This potential to disrupt natural digestive processes points to the effectiveness of coffee at inducing bowel movements.
It is common for people to discover the potential of coffee as a laxative when drinking this beverage over long periods of time. As many people drink coffee at the same time every day, coffee can be very effective at regulating a person's bowel movements. The use of coffee as a laxative is usually not as violent or harsh as laxatives purchased in pharmacies. As such, some people never realize the source of their regular bowel movements after consuming this drink with breakfast.
For people with certain conditions, coffee can actually cause constipation. One of the ways this works is by making a person dehydrated, which in turn causes constipation. It is uncommon for people to experience constipation due to an allergy to the coffee itself, but some people do experience this condition as a reaction to milk or creamer that is drunk with the coffee. Likewise, some people react badly to the caffeine in coffee but find that decaffeinated coffee does not cause constipation.
The use of coffee as a laxative is actually independent from its caffeine content. Even decaffeinated coffee has been shown to stimulate peristalsis and perform effectively as a laxative. Drinking decaffeinated coffee can help avoid some of the dehydration associated with coffee while retaining the stimulating effects, potentially providing a more effective laxative for some people.
All of the above uses of coffee as a laxative depend on oral consumption of liquid coffee. Other methods of consuming coffee, such as through a colon cleanse, are also thought to have some laxative effects. People who practice coffee cleanses claim that the same stimulating effects occur when the coffee is administered rectally, but there is little medical evidence to support this hypothesis.