DEAR DR. DONOHUE: For two years the doctor had me on a blood thinner – Coumadin. Medical books don’t call it a blood thinner. I know a lot of people have to take it, but don’t know the truth about it. When I took it, I felt weak and could not eat green vegetables, so I quit on my own. Now I feel a lot better. Tell me all of its side effects. – V.G.

ANSWER: Coumadin (warfarin) is popularly called a blood thinner, but it doesn’t actually thin blood. It prevents clots from forming. That’s its “thinning” action.

Its side effects are few. It can cause skin rashes, hives and abdominal cramps. In a handful, it has caused liver damage, which usually reverses when the drug is stopped.

Coumadin’s major problem is that it has to be monitored closely so the blood doesn’t completely lose its ability to form clots. If it does, bleeding from a relatively minor cut can assume major proportions.

Clotting factors are blood proteins that assist in forming a clot when a blood vessel breaks. Vitamin K is essential for production of clotting factors. Coumadin interferes with the action of vitamin K, so there is a relative deficiency of vitamin K, and that’s how it stops unwanted clots from forming. Green, leafy vegetables are a source of vitamin K. If people on Coumadin eat large quantities of green, leafy vegetables, they can negate its action, but there doesn’t have to be a complete ban on those vegetables. For example, it takes 9 ounces (250 grams) of spinach or broccoli to undo Coumadin’s clot-preventing capability.

I do want to worry you. Call your doctor and tell him or her what you have done. Coumadin isn’t prescribed for frivolous reasons. Atrial fibrillation, a common erratic heartbeat, is one setting for clot formation. Parts of those clots can break off the main clot, travel to a brain artery and cause a stroke. If you have a condition like this, you would be well-served to put up with the minor fuss of having to take Coumadin.

DEAR DR. DONOHUE: My blood pressure was 180/110. With medicine and exercise it is now 125/55. I read where you said a pulse pressure of greater than 60 was not good. What can I do to lower my pulse pressure? – G.B.

ANSWER: Pulse pressure is the difference between systolic and diastolic pressure. A large pulse pressure is an indicator of heart disease. That doesn’t apply to treated blood pressure. You don’t need to do a thing.

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.