DEAR DR. DONOHUE: My dentist is having a fit because I take Boniva for osteoporosis. He talks about something called BON, which means degeneration of the jawbone. My arthritis specialist is, in turn, having a problem with my not taking it. Who do I listen to? — M.C.

ANSWER: BON is bisphosphonate-associated osteonecrosis. Osteonecrosis is bone death. Bisphosphonates are the very popular drugs used to treat osteoporosis. They are Actonel, Boniva, Fosamax and Reclast. They bring more calcium into bones, like repairmen reinforcing the weakened supports of a building. Their safety record has been good. In a small number of patients, they cause the death of a relatively small patch of the jaw’s bone. Without denial, it happens, but it happens mostly to those using these drugs in high doses and intravenously for bones riddled with cancer. And it happens when a major dental procedure, like a tooth extraction, must be done.

It’s a complication that all should be aware of. However, it should not be a source of such great worry that treatment of osteoporosis is neglected. If I had to choose between bisphosphonate treatment for osteoporosis or not using those drugs because of the very small risk of osteonecrosis, I would choose treatment without hesitation.

If the thought of BON makes you extremely uneasy, then you can ask for other treatments — Forteo and Miacalcin, for example. And don’t forget to get the recommended amounts of vitamin D and calcium, along with exercise.

DEAR DR. DONOHUE: We are advised to destroy medicines that have gone past their expiration date, have been replaced by other drugs or have been stopped by the doctor. Many hold on to these medicines in case they get sick again. I understand that most lose their potency. Can you tell me which ones might be a danger after their expiration date? — C.P.

ANSWER: Expiration dates for medicines are set by law. A date two years after the drugs have been manufactured is the expiration date. However, most states require pharmacists, when they open a batch of drugs to fill a prescription, to set an expiration date of one year later.

No evidence exists that outdated medicines are harmful or toxic. Loss of potency, however, can occur.

A while back, the Army conducted a large study of when medicines lose their strength. The results were that most medicines remained stable and active for an average of 57 months beyond their expiration date. Exceptions to that rule are nitroglycerin (the angina medicine) and EpiPen, the self-injected medicine used to quickly end a severe asthma attack or an allergic reaction in which blood pressure drops and the person is in danger of death.

The longevity of medicines also depends on how they are stored. They should be kept in their original container and in a cool, dry place. The bathroom is not a good place for medicine storage. Heat, light, humidity and temperature fluctuations speed the deterioration of medicines.

People shouldn’t hang on to medicines for future use. They can mistake current symptoms for the symptoms of a past illness. Secondly, all medicines have side effects that are balanced against the good they give when properly used. If improperly used, the side effects make medicine use a possible hazard.

DEAR DR. DONOHUE: I have age spots (brown spots) on my face and hands. Can I do anything to lighten them or get rid of them? — L.R.

ANSWER: Age spots are also called liver spots. The liver has nothing to do with them. Age and the effects of sunlight do. They are clumps of skin cells filled with melanin, the pigment that gives skin its color. Sunblock, worn year-round, will prevent new spots from forming. Hydroquinone is a bleaching agent that lightens them. It comes as a 2 percent cream in products with the brand names of Eldopaque, Esoterica and Solaquin. For the 4 percent formulation of hydroquinone, a prescription is required. The acne medicines Retin-A and Renova lighten these spots, too. So does a cream, Tri-Luma, that contains three ingredients: cortisone, tretinoin (Retin-A) and hydroquinone — a triple threat, so to speak. Retin-A, Renova and Tri-Luma are prescription medicines.

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.