DEAR DR. DONOHUE: My wife has been coughing for a good month. The cough makes her miserable and makes her miserable to live with. What kind of cough medicine would you recommend? – K.J.

ANSWER: I don’t want to recommend any cough medicine before your wife finds out why she’s coughing.

Coughs serve a useful purpose. They clear mucus and foreign matter from the airways. Receptors in the nose, throat and bronchial tree trigger a reflex cough when they detect any irritants in those structures.

Most coughs are from viral infections, and most are gone in a matter of weeks. Sometimes, coughs are bacteria-caused, and then they merit antibiotic treatment.

Coughs that linger, like your wife’s cough, are a matter of concern, and the search for a cause must be undertaken in earnest.

The most fearsome cause is cancer. It is not the most common cause, but it is the issue that has to be put to rest swiftly.

Asthma is another cause of chronic cough. There are people whose only asthma manifestation is cough. Those people are treated with asthma medicines and not cough medicines. This can occur late in life.

Postnasal drip – the nonstop trickle of mucus down the throat – activates cough receptors and is a frequent nighttime cough cause. Its treatment entails cortisone nasal sprays to soothe air passages and antihistamines to dry the mucus flow.

Medicines are another cause of cough. The classic examples are the blood pressure medicines called ACE inhibitors.

Your wife needs an X-ray, possibly a scan and possibly a scope examination of her airways. If she wants a medicine during this search period, have her get one with dextromethorphan. It is usually effective.

DEAR DR. DONOHUE: My husband’s potassium has been high, and he is on some food restrictions. What effect does potassium have in the body? What is its function? – A.P.

ANSWER: Without potassium, nerves cannot fire. Muscles need it in order to contract. It keeps the heart beating regularly. Potassium directs the flow of fluid and minerals into and out of all body cells.

The kidneys are responsible for keeping body potassium stores at optimum levels. If there is too much of it, the kidneys filter potassium into the urine; if there is too little, they hold on to it.

The adrenal glands also figure into the maintenance of normal body levels.

In medicine, attention to potassium usually is directed at correcting low blood levels, and often the reason for the potassium deficit comes from the use of diuretics – water pills. Many of them take potassium out of the body when they take fluid from it.

A baked potato with skin is the emperor of potassium-rich foods. Halibut, salmon, figs, yogurt, raisins, bananas, oranges, orange juice, squash, spinach and tomato sauce are other sources.

Potassium and sodium puzzle many people. The pamphlet on those minerals can be ordered by writing to: Dr. Donohue – No. 202, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.50 U.S./$6.50 Can. with the recipient’s printed name and address.

Please allow four weeks for delivery.

DEAR DR. DONOHUE: I have a dear friend who has cancer, and there is spread of it to her lungs. That causes breathing complications. She doesn’t want oxygen because she is concerned that her lungs will become lazy and rely on oxygen forever. I told her how serious oxygen deprivation is and how it can cause organ failure. Please answer quickly so I can forward your answer to her. – D.R.

ANSWER: Every patient is entitled to make the decisions on what his or her treatment should be. However, when a person bases the decision on erroneous information, someone ought to step in and try to furnish the truth. You are that someone. Oxygen does not weaken lungs, nor does it make them dependent on supplemental oxygen forever. A body without sufficient oxygen is gravely stressed.

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.