The football player Terrell Owens blamed his recent trip to the hospital on a bad mix of painkillers and a supplement. The son of Anna Nicole Smith reportedly died with a mixture of the antidepressants Lexapro and Zoloft and the drug methadone in his system.

The veracity of these incidents is yet to be determined. But the danger of mixing drugs, supplements, and/or alcohol is very real.

At least 1.5 million people in the U.S. are harmed annually by medication errors, according to a report issued in July 2006 by the Institute of Medicine.

Reducing your risk, experts agree, is often a matter of using common sense and asking your doctor or pharmacist the right questions. WebMD asked a pharmacist, two doctors, and a nurse to weigh in on the most common mistakes that lead to medication errors and to suggest practical ways to minimize or eliminate the risks.

Report: Drug Errors Injure 1.5 Million

1. Mixing Drugs That Interact Adversely

"Antidepressants and methadone together can be a real problem," says Russell Jenkins, MD, a member of the board of directors for the Institute for Safe Medication Practices in Huntingdon Valley, Pa., and a former primary care doctor for 27 years. "Each drug can increase the sedative effect of the other."

"Painkillers and supplements can be a problem, because you don't know what is in the supplements, since they are not under [the same] Food and Drug Administration regulation [as drugs are]," he adds.

Certain other combinations -- even if one of the drugs is over-the-counter -- should also be avoided.

Many antibiotics reduce the effectiveness of oral contraceptives, says Matthew Grissinger, RPh, a pharmacist and education safety analyst at the Institute for Safe Medication Practices. "Use backup protection if you are on the pill and need an antibiotic."

The blood thinner Coumadin, taken by people with blood clots or with heart valve conditions, shouldn’t be mixed with ginseng, says Jenkins. Nor should it be used with aspirin, says Grissinger.

"It's an additive effect," he says of the Coumadin-aspirin combination. "It increases your chance of internal bleeding or, if you get a cut on your finger, the blood won't clot as quickly."

Indeed, there are many drugs and supplements that are off-limits when you are taking Coumadin.

If you have elevated blood pressure, even if you're on medication to control the pressure, you should not take over-the-counter oral nasal decongestants without talking first to your pharmacist or doctor, Grissinger says. The preparations can raise your pressure.

Medical Errors Still Plague U.S. Hospitals

2. Mixing Drugs and Alcohol

"Prescription pain medicines and antianxiety medications such as Valium and Xanax can have an additive effect when mixed with alcohol," says Grissinger. "You won't be alert. Your driving response time will suffer. Don't mix these together."

Another drug that shouldn't be mixed with alcohol: acetaminophen (Tylenol) and alcohol, because it can harm your liver.

Cough and cold preparations with antihistamines shouldn't be mixed with alcohol because they will amplify the sedative effects, Grissinger says.

This warning applies to the use of narcotic pain medications, too.

"Be careful mixing alcohol with certain antibiotics," says Jenkins. "The main antibiotic-alcohol interactions are with metronidazole (Flagyl) and the sulfa drugs -- commonly used antibiotics." An example of a sulfa drug is Bactrim.

Mixing metronidazole and alcohol can cause nausea, vomiting, flushing, headache and stomach pain, Jenkins says.

3. Leaving the Doctor's Office Without Enough Information

"When you leave your doctor's office, you need to know the name of the medication and what it is for," says Grissinger. Ask how many times a day you should take it, he adds, and how you might react.

"Ask for written instructions," says Jenkins. "At the doctor's office, people only remember about a third of what the doctors tells them," he says, citing several studies.

4. The Wrong Prescription From the Pharmacy

There's plenty you can do to reduce this risk. First, how it happens: "A pharmacist may not be able to read the doctor's handwriting," Grissinger says. To remedy this, ask your doctor to write down on the prescription pad what the drug is for. That way, if the drug is one of many with sound-alike, look-alike names, your pharmacist can double-check that he's giving you the right drug by looking at the drug's purpose.

Always check your medications before leaving the pharmacy to be sure it's your name on the bottles, Grissinger says. "If you are picking up a refill, open the bottle in front of the pharmacist and make sure the pills look the same. If they don't, ask why not." It might be as simple as the health plan changed manufacturers, he says, but check to be sure.

5. Using Multiple Pharmacies

"If you go to multiple pharmacies, they can't screen for drug interactions," Grissinger says, because they won't have a complete list of all the medications you are on, as a single pharmacy is likely to keep in its computer. If you use your HMO's ground pharmacy and also use its mail-order service, each may not have a list of the medications filled at the other, he says.

If you insist on using multiple pharmacies due to convenience or cost savings, "show them a list of every medicine you take," Grissinger says.

If you go to another health care professional -- for example, a dermatologist in addition to your primary care doctor -- they should ask you which other medications you are on before prescribing you another. But if they don't, be prepared to tell them. Either way, take a list of your medications and the doses with you, says David W. Bates, MD, chief of the division of general medicine at Brigham and Women's Hospital and professor of medicine at Harvard Medical School. Bates served on the Institute of Medicine committee on identifying and preventing medication errors.

6. Not Taking Medications as Directed

"Compliance is a major problem, especially in the elderly," Jenkins says. "As many as one-third of older people don't take medicines as directed." It may be cost related, he says, or simple forgetfulness. The more times a day you need to take the medicine, the higher the likelihood of total compliance. "If you order a medication to be taken four times a day, less than 50% of people will comply with that," he says, citing research.

What to do? You can use the boxes that help mind your pills by having a day of the week for each, or simply put your medicines in a place where you will remember to take them. Grissinger's mother, for instance, keeps medication she must take daily on the kitchen windowsill, in full view.

When medicine is prescribed, Jenkins says, ask your doctor if there is a way to take the medicine less often during the day, such as switching to a higher dose or a different medicine that doesn't require as many doses.

While some forget to take medicines, others overdo, says Bates. "Too much of a drug gets people into trouble," he says. And that includes over-the-counter preparations. "People will not get enough relief and will take more thinking it will be helpful." Often, it spells trouble, he says.

7. Not Asking Enough Questions as a Hospitalized Patient

Each year, about 400,000 preventable drug-related injuries occur in U.S. hospitals, according to the Institute of Medicine report.

Speak up, or ask a family member to do so for you, suggests Kathleen R. Stevens, EdD, RN, professor and director of the Academic Center for Evidence-Based Practice at the University of Texas Health Science Center in San Antonio. Stevens also served on the Institute's committee.

"The most common 'error' is not getting a drug at the right time," she says. "Some drugs are very time-sensitive."

In addition to keeping track of when it's time to get medicine, or asking a family member to help, there are other questions worth asking, she says. When a nurse or aide brings in medicine, she says, ask: "What is this for? What can I expect in terms of responding? Is it not indicated for use with any of the other medications I have?"

You should expect a nurse to ask your name and check your wristband ID before giving you medication, according to the Institute for Safe Medication Practices.

Stevens tells patients to bring to the hospital (or have a family member, if it was an emergency admission) all the medications you are on, including the dose of each.

By Kathleen Doheny, reviewed by Louise Chang, MD

SOURCES: Matthew Grissinger, RPh, education safety analyst, Institute for Safe Medication Practices. Russell Jenkins, MD, Institute for Safe Medication Practices. Kathleen R. Stevens, EdD, RN, professor and director, Academic Center for Evidence-Based Practice, University of Texas Health Science Center, San Antonio. David W. Bates, MD, chief of the division of general medicine, Brigham and Women's Hospital; professor of medicine, Harvard Medical School, Boston. Institute of Medicine of the National Academies report: "Preventing Medication Errors," July 20, 2006. Institute for Safe Medication Practices.