By:   Leslie Pepper

Americans rely on prescription and over-the-counter medicines to solve our physical and mental maladies. In fact, almost four billion prescriptions are filled by U.S. pharmacies every year.

But that doesn't mean we're doing it right. You could be falling prey to some common medicine mistakes -- misfires that can affect your pocketbook, cause unnecessary side effects, or even produce something downright dangerous. 

Every year, nearly 700,000 people end up in emergency rooms due to adverse drug events (the technical name for screwing up your meds) according to The Centers for Disease Control and Prevention (CDC).

Here are eight medication mistakes you might be making:

You're taking an antibiotic you don't need
According to the CDC, more than half of all antibiotics prescribed for coughs and colds are unnecessary. Why? Antibiotics are used to knock out bacteria, but viruses are what cause most coughs and colds, not bacteria. Antibiotics are useless in the face of viruses.

"Giving an antibiotic to someone with a cold is like giving a hammer to a glassmaker," says Gary Rogg, MD, an assistant professor in the department of medicine at New York's Montefiore Medical Center. "Not only is it the wrong tool, but it's potentially destructive," he adds.

If you pop antibiotics too frequently, they may not work the next time you actually need one because antibiotics only kill off some bacteria -- enough to make you feel better. The ones that remain mutate and multiply, becoming stronger and stronger – and more resistant – to antibiotics.

You're springing for the name brand, thinking it's superior to generic
Sometimes it pays to splurge – like when we're talking about real Louis Vuitton versus a knock-off. But when you're dealing with drugs, the generic contains the same active ingredient, works just as effectively, and meets the same standards for purity and quality, says Janet P. Engle, Pharm.D, a professor at the University of Illinois at Chicago College of Pharmacy. 

Why are brand name drugs more expensive? It can cost tens of millions of dollars in research, development, marketing and promotion to develop a new drug, so the manufacturers have to jack up the price in order to recoup their costs. But after the drug patent expires, other manufacturers can make a generic version for far less because they don't have to cover any of the development or start-up costs. 

You're getting a great deal buying online
This is one time where it does pay to splurge. Lots of websites sell medicine on the cheap, but you don't truly know what you're dealing with. Anyone can create a  pretty website with bells and whistles, and they can easily claim they're operating out of Canada when they're really in a backyard garage in Bangladesh. 

With these rogue sites,  there's no guarantee that the drug you paid for is the one you're going to get.  They may have too much, too little, or even none of the active ingredient you need.

That being said, there are legitimate pharmacies that sell online. Look for state licensed pharmacies based in the United States that have the VIPPS seal. That means they're a Verified Internet Pharmacy Practice Site, which ensures that it's a quality, bona fide pharmacy. Vipps.info has a comprehensive list and more information, including the phone numbers for all state Boards of Pharmacy.

You're not following directions
Some medications should be taken with food. Others are best taken on an empty stomach. Some pills should be swallowed whole and others chewed. Some medicines can be dangerous if taken with the wrong foods. Grapefruit, for instance, can increase the concentration of some blood pressure medications and heighten the side effects of certain cholesterol lowering meds.

If you don't understand something your doctor has said, don't be afraid to ask for more explanation. "I've heard stories of women who used vaginal suppositories with the foil on, because they didn't understand the packaging," says Engle.

Discuss with your doc exactly how you should take your medicine, what time of day you should take it, and how long you should be on it. And don't forget to ask what you should do if you forget a dose. (Skip it? Double up the next time?)