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updated 12/18/2007 8:26:30 AM ET 2007-12-18T13:26:30

Viewers of the medical drama "House" have come to expect bizarre explanations for every symptom: A sudden case of the sweats might be the work of a 20-foot tapeworm. Or a hidden brain tumor. Or a 20-foot tapeworm with a hidden brain tumor.

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If "House" mirrored real life, many episodes would center around a mundane culprit: a drug interaction. As Americans take more and more medications for everything from skittish stomachs to sluggish moods, clashes between drugs have fueled a new epidemic of unexpected, sometimes dangerous side effects and complications.

One recent study suggested that at least 1.3 million Americans have prescriptions for drugs that could cause problems if taken together — and that only counts people with health insurance. Although the overall toll is unknown, it's undoubtedly huge, experts say ... and growing.

Of course, if you take many medications at the same time, or large doses of a few, you're more likely to run into a bad pairing, says Marietta Anthony, PhD, associate director of the Center for Education Research and Therapeutics at the University of Arizona. But even common items like drugstore pain relievers can clash with other meds. Scan our list: If you spot your prescription, be extra alert for signs of possible conflicts; then, talk to your doctor. And check our easy switches — you may be able to take a safer combo.

If you take...

An SSRI for depression

Selective serotonin reuptake inhibitors such as fluoxetine (Prozac), paroxetine (Paxil), or sertraline (Zoloft)

One possible conflict: A triptan drug used to treat migraines, such as sumatriptan (Imitrex), naratriptan (Amerge), or zolmitriptan (Zomig)

Why: Triptans and this type of antidepressant both increase levels of the brain chemical serotonin. But too much serotonin can set off a chemical firestorm known as serotonin syndrome, causing mania, an increased heart rate, seizures, and even death. The syndrome is rare, but the threat is real, says John Horn, PharmD, a professor of pharmacy at the University of Washington and coauthor of The Top 100 Drug Interactions. In 2006, the FDA issued an advisory to the roughly 50,000 Americans who take both SSRIs and triptans. The advisory told users they didn't have to stop taking the drugs but cautioned them to be aware of the risk.

Protect yourself: Most patients can continue taking both triptans and SSRIs as long as they watch for signs of serotonin syndrome, Horn says. If you notice troubling symptoms, stop taking the triptans and check with your doctor right away.

Another possible conflict: Chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen.

Why: You may have heard that long-term use of NSAIDs can cause bleeding ulcers and other stomach troubles. What's less widely known is that adding an SSRI increases the risk. Serotonin is the culprit here, too. Normally, that hormone encourages blood platelets to stick together —but because platelets soak up less serotonin when you're on an SSRI, they may have trouble performing their number one job: clumping together to form clots and prevent excessive bleeding in the stomach and elsewhere.

Protect yourself: Even if you take an SSRI, it's fine to pop a couple ibuprofen or aspirin for an occasional headache. But if you need several doses of a pain reliever each day — a common regimen for people with arthritis--take acetaminophen instead. It's not an NSAID, and it doesn't encourage bleeding.

If you take...

Blood pressure medication

Specifically ACE inhibitors, such as benazepril (Lotensin), or diuretics, such as furosemide (Lasix) or hydrochlorothiazide (HCTZ)

Possible conflict: Chronic use of NSAIDs, such as aspirin or ibuprofen

Why: If you take daily NSAIDs, your painkillers could keep these kinds of blood pressure medications from doing their job. These drugs work by ridding the body of extra salt or water, or by shutting off production of a hormone that prompts blood vessels to narrow. If taken regularly, NSAIDs can block both of these actions--and the blood pressure benefit.

Protect yourself: If you experience problems, you have two options (ask your doctor which is right for you). "You can switch to a different blood pressure medication," Horn says: BP drugs called calcium channel blockers (such as amlodipine, or Norvasc) aren't deterred by NSAIDs. Or swap the pain relievers--use acetaminophen instead.

If you take...

A quinolone antibiotic

Such as ciprofloxacin (Cipro), ofloxacin (Floxin), or levofloxacin (Levaquin) to treat a urinary tract infection, traveler's diarrhea, or other problem

Possible conflict: Over-the-counter antacids containing calcium, magnesium, or aluminum, like Tums, Rolaids, Maalox, or Mylanta

Why: Quinolone antibiotics have an unhealthy attraction to the metals in common antacids. Magnesium, aluminum, and (to a lesser extent) calcium quickly glom on to the germ killers, rendering them much less effective. Protect yourself: You don't have to put up with a sour stomach while you're battling an infection. Simply wait an hour or two after taking your antibiotic before reaching for the antacid.

If you take...

A common cholesterol drug

Specifically lovastatin (Mevacor), simvastatin (Zocor), or atorvastatin (Lipitor) Possible conflicts: Macrolide antibiotics, such as clarithromycin (Biaxin) or Erythromycin Azole antifungals taken orally, such as the prescription drugs ketoconazole (Nizoral) and itraconazole (Sporanox)

Why: Some antibiotics and antifungals can block enzymes that help break down these specific cholesterol drugs. As a result, you may end up with 4 to 10 times more cholesterol medication in your blood than your doctor intended--enough to greatly increase your risk of muscle or kidney damage.

Protect yourself: You can simply take a break from Mevacor or Zocor if you need one of these specific antibiotics or antifungals, Horn says. (Once your infection clears up and you're off those drugs, you can safely go back to your cholesterol medication.) Or your doctor may be able to prescribe a different remedy for your infection.

If you take...

A corticosteroid for asthma, hay fever, or other allergies such as budesonide (Pulmicort, Rhinocort) or prednisone (Liquid Pred)

Possible conflicts: Antibiotics Antifungals Antidepressants A calcium channel blocker for blood pressure--specifically diltiazem (Cardizem) or verapamil hydrochloride (Calan)

Why: When you take a corticosteroid--whether in a pill or via inhaler--you depend on certain enzymes in your body to break the drug down after it's done the job. But recent studies suggest that a number of other medicines can block the action of these enzymes, potentially leading to a corticosteroid overdose, Horn says. That can cause Cushing's syndrome, in which you can gain weight in your upper body and develop hypertension, bruising, weakness, depression, acne, and excess hair growth.

Protect yourself: The risk is greater if you're taking the corticosteroid in pill form (inhalers deliver a lower dose) or if you add a pill to your inhaler regimen, as people sometimes do for an allergy flare-up. Ask your doctor if any of your other medications could potentially slow the breakdown of the drug. Cushing's syndrome is reversible, but you don't want to suffer any longer than necessary.

One safety valve: It takes time for corticosteroids to build up to toxic levels, so a short course of an antibiotic or antifungal shouldn't cause trouble.

If you take...

An over-the-counter stimulant laxative Such as Senokot or Dulcolax

Possible conflicts: Blood pressure medications Antiseizure drugs, such as phenytoin (Dilantin) Antibiotics The blood thinner warfarin (Coumadin) The heart medicine digoxin (Lanoxin)

Why: Many medications need plenty of time to be properly absorbed, but stimulant laxatives can rush them through your system. The result: You may not get the benefit of a crucial prescription.

Protect yourself: Talk with your doctor before adding a stimulant laxative to your routine. Generally, you can stay on the safe side by taking it at least 2 hours before or after any other medications.

If you take…

The blood thinner warfarin (Coumadin)

Possible conflicts: NSAIDs (including aspirin and ibuprofen) Antibiotics--specifically metronidazole (Flagyl), trimethoprim/sulfamethoxazole (Bactrim), or quinolone antibiotics such as ciprofloxacin (Cipro) Antiseizure drugs

Why: Some of these meds multiply the effects of warfarin, greatly increasing the risk of uncontrolled internal bleeding.

The reason: NSAIDs keep platelets from sticking together, which--like warfarin--interferes with the clotting of blood. And certain antibiotics slow the enzyme that breaks down warfarin, also raising the risk of increased bleeding. On the other hand, antiseizure drugs can speed the breakdown of warfarin: Your blood can get too thick, causing a dangerous clot.

Protect yourself: Interactions involving warfarin are relatively common and can be very serious. If you're on warfarin, don't take any other medication unless your doctor says it's okay.

Copyright© 2012 Rodale Inc.All rights reserved. No reproduction, transmission or display is permitted without the written permissions of Rodale Inc.

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