You don't say what type of laxatives you're using. Overuse is of most concern when the laxatives in question are the "irritant types" such as Ex-Lax and Feen-A-Mint or the herbal irritants cascara sagrada (Rhamnus purshiana) and senna (Cassia acutifolia). Chemicals and herbs that induce bowel movements quickly, sometimes violently, by irritating the bowel, can cause cramps and diarrhea and lead to laxative dependence, resulting in worse constipation than was present in the first place. Saline laxatives such as milk of magnesia and Epsom salts that work by drawing water into the colon are safer but can also cause problems with chronic use. And those containing mineral oil, such as Haley's M-O, can cause toxicity.
The safest laxatives are the bulk-producing ones such as Metamucil and Citrucel. The bowel regulator I recommend most frequently is triphala, a mixture of three fruits from India from the Ayurvedic tradition, available in capsule form at health food stores. Follow the dosage directions on the label. You can take it regularly; its benefits accumulate the longer you stay on it. A low dose of magnesium glycinate may also be helpful for chronic constipation.
However, most importantly, you should consider the factors that contribute to constipation. Are you getting enough fiber in your diet? Make sure you're eating lots of vegetables, wheat bran, whole-grain breads and cereals and fruit. If you can't get enough fiber from your diet, consider powdered psyllium, available at health food stores, as a quality source of supplemental fiber. Start with one rounded tablespoon of the powder stirred well into a glass of water or diluted juice. Drink it down and follow with another full glass of water. Be sure you're drinking plenty of water, getting daily exercise, avoiding caffeine and tobacco.
Try to wean yourself away from laxatives gradually, first going for one day out of four without taking any. You also might consider acupuncture, which may help with this process. Good luck!
Andrew Weil, M.D.