DEAR DR. DONOHUE: Recently I found out through lab reports that I am almost completely out of the hormone testosterone. Nobody ever talks about this problem. Will you write something about it? What causes it? I am 54. Now I am taking a testosterone drug. —M.P.

ANSWER: The testes make the male hormone testosterone. It’s responsible for the development of male characteristics — facial hair, deep voice, muscle and bone growth, and the maturation of sex organs. A surge of testosterone takes place at puberty, and production continues throughout life. Aging is the principal cause of a diminution in its production. An 80-year-old produces only half the amount that a 20-year-old produces. Fifty-four is far too young to have no testosterone.

Infections of the testes, like mumps, can turn off production. So can excessive drinking of alcohol. An autoimmune attack on the testes, starvation, hemochromatosis (an illness in which iron infiltrates the testes), prolonged use of cortisone, kidney failure and a number of inherited conditions are other reasons for a decline in testosterone. I think I understand you to be saying you have none of these. Then that puts you in the category of idiopathic low production. “Idiopathic” is a word often used in medicine. It means “I don’t know.”

Signs of having too little testosterone include a loss of interest in sex, a diminution of energy and a shrinkage of muscles. Testosterone blood levels are measurable. Normally, the height of daily production occurs in the morning. The best time to have blood drawn for testosterone assay is around 8 a.m.

Replacement isn’t an onerous task. There are many effective testosterone preparations.

DEAR DR. DONOHUE: I am 59 and have been active all my life. I am 5 feet 6 inches tall and weigh about 135 pounds. I participated in the 1972 U.S. Olympic trials for the 10,000-meter run.

My right hip has bothered me for many years. X-rays show that bone is rubbing against bone. I have quit running. I researched a procedure called hip resurfacing, and believe this route would be better than hip replacement for me. I would appreciate your opinion. — D.A.

ANSWER: Hip resurfacing isn’t new. It was introduced more than 40 years ago, but interest in it waned because less-than-satisfactory results were obtained. Now, with new materials and different techniques, interest has resumed. It’s an attractive alternative for many people with hip problems.

Patients are carefully selected. They must have strong bones. Imagine the hip joint by making a fist with your right hand and covering the fist with your left. The fist represents the top of the femur (the thigh bone), a ball affair that fits into a socket (the covering left hand) on the pelvis. The two comprise the hip joint. In hip resurfacing, the surfaces of each are shaved in order to smooth them. The ball of the femur is covered with a metallic cap and a metallic cup is placed in the pelvic socket. This is less surgery than a standard hip replacement, but it is difficult surgery.

In six weeks postoperatively, people are walking, biking and swimming. In a year, they can do just about anything they want, including running. I can see why this procedure would suit you.

DEAR DR. DONOHUE: What is the difference between medical marijuana and regular marijuana? How long does it stay in a person? Some say marijuana has no side effects. Is that so? — D.P.

ANSWER: The two are exactly the same. “Medical” marijuana is used to treat medical conditions — pain, nausea, the side effects of cancer medicines, glaucoma and epilepsy.

Marijuana is detectable in the urine of heavy users for up to four weeks. Smoking a single marijuana cigarette is detectable for four days.

Marijuana does have some unpleasant side effects, but they are not common in casual users. It can cause gum disease, lung problems, memory deficits and learning difficulties.

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.