DEAR DR. DONOHUE: I had a pulmonary embolus and am now taking Coumadin.

My blood tests have been good, and I haven’t had to change the dose of medicine up or down.

My brother also takes Coumadin, and my sister-in-law tells me that he has been told not to eat lettuce or vegetables like lettuce. My doctor never said a word to me about this. I am a salad-eater. Should I stop eating salads? – E.W.

ANSWER: Your question deserves an explanation of what’s going on.

Coumadin is a blood-thinner. Every time I call it that, purists cringe. It doesn’t thin the blood. It prevents clots from forming inside blood vessels.

People are put on Coumadin for many reasons. Those who have the heart rhythm called atrial fibrillation take it. Clots form in their fibrillating hearts and can be carried to brain arteries, where they plug arteries and cause a stroke. People in your situation, ones who have had a clot in their lungs (pulmonary embolism), are also put on Coumadin to prevent a recurrence.

This medicine works by interfering with the action of vitamin K. Vitamin K is essential for the production of clotting factors, proteins that are integral for clot formation. Coumadin antagonizes the action of vitamin K, so clotting factor production slows and clots don’t form.

If Coumadin takers ingest large amounts of vitamin K, they override Coumadin’s suppression of clotting factor production, and those people are in danger of forming another clot.

Foods rich in vitamin K include parsley, chard, Brussels sprouts, broccoli, turnip greens, watercress and lettuce.

If a person eats a consistent amount of vitamin K foods and if that person’s blood test show that Coumadin’s blood level is within a desired range, he doesn’t have to make any diet changes.

Coumadin users should not, however, gorge on vitamin K-rich foods.

DEAR DR. DONOHUE: Constipation is my only health problem. I take lots of fiber.

My doctor told me to use Colace. I do, and it works wonders for me.

Will I become immune to it or addicted to it? – B.P.

ANSWER: Colace keeps undigested food moist by drawing water into it as it passes through the digestive tract. You won’t become immune to it, and your colon won’t become addicted to its use. Take it for as long as you need to.

The booklet on constipation discusses Americans’ No. 1 health concern in depth.

Readers can order a copy by writing: Dr. Donohue, No. 504, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address.

Please allow four weeks for delivery.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com