Most physicians and pharmacists have a secret they don't share with patients. The Food and Drug Administration is in on it, and so are drug companies. One out of five of the prescriptions written in this country are for unapproved uses. Some put the number much higher.

Most Americans assume that whenever their doctor prescribes a drug, it has been extensively tested and proved to be both safe and effective for their condition. They're wrong. In reality, many medications are prescribed without this supporting evidence.

When a pharmaceutical company submits a medicine to the FDA for review, it must prove that the compound works and that the benefits outweigh the risks for one particular ailment.

Once that drug receives approval for that particular indication, doctors can prescribe it for anything else, as they see fit. This is called "off-label" prescribing. The FDA does not regulate the practice of medicine, leaving doctors free to make decisions on their own.

Until now, the FDA has not allowed drug companies to promote off-label uses of their products. In fact, some manufacturers have gotten themselves into big trouble when they stepped over the line. Pfizer was slapped with a $430 million fine because it was promoting Neurontin, a drug approved to control epileptic seizures, for a range of other problems, including pain, bipolar disorder, restless legs, amyotrophic lateral sclerosis --also known as Lou Gehrig's disease -- attention deficit disorder and migraines.

Some medicines commonly prescribed for unauthorized purposes include the schizophrenia drug Risperdal for Alzheimer's dementia, the antidepressants Prozac and Zoloft for premature ejaculation, and beta blocker heart medicines such as atenolol and propranolol for stage fright.

What's wrong with off-label prescribing? For some conditions, unauthorized prescribing may be appropriate. Without rigorous scientific studies, however, doctors have no way to evaluate the benefits and risks of unauthorized uses. It has been estimated that three-quarters of the prescriptions for off-label uses are not backed up by solid evidence, according to the Archives of Internal Medicine in May 2006.

That puts patients in the position of being guinea pigs. They are unwitting experimental subjects, but no one is collecting data or protecting their safety. This kind of prescribing can lead to serious adverse reactions or even death. This has happened when anti-psychotic medications were prescribed to older patients with senile dementia.

The FDA is preparing to change the rules that regulate how the pharmaceutical industry promotes off-label indications. Companies will be allowed to give doctors copies of journal articles mentioning drugs for unapproved purposes. With such a green light, manufacturers could easily overwhelm busy doctors with promotional messages about uses for which drugs have not been thoroughly tested.

Drug companies understandably emphasize the positive and downplay bad news. When two studies produce contradictory findings, will sales representatives show doctors both of them? The track record is not reassuring.

More alarming, though, is the message that the FDA is sending the pharmaceutical industry. No longer will firms have to fund expensive research to prove their medicines work for off-label purposes. Without such studies, patients will be even more vulnerable than they already are.

Q: I rarely take medicine, but this winter I have had sinusitis and a nasty cough that required several medications. My enlarged prostate gets me up to go to the bathroom a few times a night, and I have trouble falling back to sleep.

I am in total shock after a trip to the pharmacy. Here is a list of my medications and the cost. My insurance has a high deductible, so this is all out of pocket: Flovent inhaler ($173.52) to ease my cough; Singulair ($126.99) and Nasonex ($102.99) for allergies; Nexium ($180.99) for reflux; Avodart ($124.99) for the prostate and Ambien ($130.99) for insomnia. Total: $840.47.

Is there any way to get these drugs more affordably? Another month like this and I'll be eating rice and beans.

A: Yikes! Without insurance, prescription drugs can bust a budget. You might want to consider purchasing some of your medicine from a legitimate Canadian online pharmacy. Doing so could save you more than $300.

Not all online pharmacies are reliable, however. We are sending you our Guide to Saving Money on Medicine with tips on identifying genuine Canadian online drugstores, plus ways to use generic drugs safely and information on accessing free medicine. Anyone who would like a copy, please send $2 in check or money order with a long (No. 10), stamped (58 cents), self-addressed envelope to: Graedons' People's Pharmacy, No. CA-99, P.O. Box 52027, Durham, NC 27717-2027. It can also be downloaded for $2 from our Web site: www.peoplespharmacy.com.

Q: I have had eczema ever since I was a child. I have used many steroid creams through the years, and while they help alleviate it a bit, those creams were not very soothing in bad bouts and just kept away the worst irritations.

I have been going to a young dermatologist who advised me to use CeraVe Moisturizing Cream (not lotion). I can't rave about it enough.

Immediately after bathing, I put it on, and 24 hours later, when I shower, I can feel that the cream is still there. I have only had to use one of the prescription creams a few times since starting with this more than a year ago. Keeping my skin hydrated seems to do the trick for me.

A: CeraVe moisturizer contains no fragrance to irritate the skin, but it does contain ceramides. These are natural fatty compounds found in cell membranes. People with eczema frequently have lower levels of ceramides in their skin. Moisturizing can help keep eczema from itching and may boost the effectiveness of topical steroids when you need to use them.

Q: About a month ago, my son-in-law started taking one regular Bayer aspirin each morning and one Bayer PM before going to sleep. Two weeks into this regimen, he started bleeding from the mouth while he was sleeping. He stopped taking the aspirin and the bleeding stopped as well. Is this a possible side effect?

A: Aspirin can thin the blood by interfering with the sticky part of blood called platelets. Some people are especially susceptible to this effect, so even a standard dose might trigger bleeding.

Q: I have read that magnesium is an important supplement, but I have no idea how much to take. Can one overdose on this element? Is it really as important as calcium?

A: Magnesium is crucial for heart and bone health and is frequently in short supply in the diet. A safe dose ranges from 300 mg to 500 mg. Too much magnesium can lead to loose stools or diarrhea.

"The People's Pharmacy with Joe and Terry Graedon" airs Saturday at 7 a.m. on WVTF (89.1) and at 4 p.m. Saturdays and Sundays on RADIO IQ (89.7).