DEAR DR. DONOHUE: I have been dizzy for six months. Things spin around. I am on a medicine for motion sickness. It works a little but not enough. How would you approach this problem? — N.N.

ANSWER: I would approach it by trying to find the cause of dizziness. It is also called vertigo. There are a dizzying number of causes — more than 20. Some are common, and it is those that merit first consideration.

At the top of the list of causes is a condition with the name of benign positional vertigo. When people with this problem move their heads, they feel as though they are on a runaway merry-go-round. The inner ear is our compass, and it keeps us in balance. In this situation, particles within the inner ear have floated into positions where they should not be. Repositioning those particles stops dizziness. The repositioning can be accomplished by the doctor performing a series of head maneuvers in the doctor’s office.

Meniere’s (main-YARZ) disease consists of episodes of three symptoms: dizziness, loss of hearing and a ringing in the ears. At first, the attacks are short-lived, and the symptoms disappear. With the passage of time, the symptoms stay longer and longer. Medicines and limiting salt are some ways to help people with Meniere’s. There are other treatments.

Viral infections of the inner ear are another cause of what can be incapacitating dizziness. Motion sickness medicines often lessen symptoms. Most inner ear viral infections clear in a matter of four weeks or so. Your story has lasted so long that it’s hard, but not impossible, to fit it into the viral infection category.

It’s time for you to visit an ear, nose and throat doctor for a definite diagnosis and specific treatment — if that is available.

Questions on dizziness and balance are frequent. Readers can obtain the whole story on these two common problems by ordering the pamphlet on those topics. Write to: Dr. Donohue — No. 801, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.50 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: My thyroid gland makes no thyroid hormone. I have to take a daily thyroid hormone pill. I have been told that regular use of thyroid hormone stops other glands from working. The gland that was mentioned was a gland in the head that controls the thyroid. I cannot remember its name. Does this happen if a person has to take thyroid tablets every day? — K.R.

ANSWER: By taking the thyroid medicine, you replace the hormone your body needs in order to keep going. Without thyroid hormone, body functions slow and ultimately stop. People feel dragged out.

Your informant alluded to the pituitary gland, located at the base of the brain. This gland is the body’s master gland. It makes hormones that tell all other body glands to increase their production. It does make a hormone involved with the thyroid gland. It is thyroid-stimulating hormone.

Your thyroid gland, however, will not up its production of thyroid hormone no matter how much stimulating hormone prods it to do so. You are giving yourself the necessary daily dose of thyroid hormone by taking your medicine. Thyroid hormone tablets stop production of the stimulating hormone, something that should be done. That’s the only way replacement thyroid hormone affects the pituitary gland. It is a normal effect.

DEAR DR. DONOHUE: We eat a lot of vegetables. I generally use my microwave oven to cook them lightly.

I have just been told that using a microwave removes most of the goodness (vitamins) from the vegetables. Do I have any reason to be concerned? — L.M.

ANSWER: Microwaving vegetables is one of the best ways to cook them. Little water is used, so only minute amounts of vitamins and minerals are absorbed by water. Furthermore, cooking time is much less than the cooking time required to prepare vegetables on a conventional stove.

Stick with the microwave. It’s giving you the maximum amount of vitamins contained in vegetables.

DEAR DR. DONOHUE: My son is 16 and is applying for a driver’s license. We just found out that he is colorblind. It’s been no handicap for him thus far, but he wonders if it disqualifies him from getting a driver’s license.

Where did this come from? Neither my husband’s nor my family has any colorblind members. It is inherited, isn’t it? — W.R.

ANSWER: An inability to appreciate red and green colors is the most common kind of colorblindness. It affects more men than women. The estimate of the number of males with colorblindness ranges from one in eight to one in 20. The range for women lies between one in 64 and one in 250.

Colorblindness is inherited. The colorblind gene lies in the X chromosome, one of the two chromosomes that determine sex. A woman has two X chromosomes. If her one X chromosome has the colorblind gene, her normal X chromosome overrides the defect. A man has an X and a Y chromosome. Having only one X chromosome leaves a boy unprotected when that chromosome carries the colorblind gene.

The condition, therefore, is usually passed by a carrier mother to her son. Carriers have the gene but do not have colorblindness.

Most colorblind people don’t live in a completely black, gray and white world. The colorblindness is one of degree. Some see muted versions of red and green.

Colorblindness won’t keep your son from obtaining a driver’s license. Colorblind people learn the sequence of red, yellow and green on traffic lights, and they can tell which light is on.

A small number of colorblind people have an associated eye disease. Even though the boy has done well all his life, an eye doctor should examine him.

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.