Americans have an unhealthy dependence on legal drugs. The federal Centers for Disease Control and Prevention (CDC) notes that 82 percent of the U.S. population is taking at least one medication, and about 30 percent are on five meds or more.

Alarmingly, many of those drugs don’t get along with each other. The wrong combination of meds can trigger potentially deadly adverse interactions. And it’s not just prescription meds — over-the-counter drugs, nutritional supplements, and even some types of food can be bad partners for pharmaceuticals.

“Drug interactions are a big problem, especially when a patient uses multiple pharmacies and the pharmacists don’t have access to all of the patient’s records,” says pharmacist Bri Morris, director of strategic initiatives at the National Community Pharmacists Association.

“There are also several over-the-counter products that may be safe for some patients, but not all.”

Morris and other experts offer some examples of how commonly used prescription drugs can adversely interact with other medications and supplements. In each case, it’s just a partial list, as the drug interaction matrix is very complex:

Antibiotics: Some nutritional supplements, such as calcium and magnesium, can curb the effectiveness of antibiotics. And antibiotics can reduce the effectiveness of birth control pills, so you could cure your bacterial infection but wind up pregnant. “That’s not an uncommon occurrence,” notes Morris.

Antidepressants: If you’re on some types of depression medication and have a headache, don’t take nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, naproxen, and aspirin. It could spark internal bleeding, especially in the digestive tract.

And that’s not all. This combo also affects levels of the mood-stabilizing hormone serotonin, causing agitation, rapid heartbeat, and other unsettling symptoms. The National Institutes of Health also warns that combining some antidepressants with the popular herbal supplement St. John’s wort can result in “potentially life-threatening” problems.

Blood thinners: The anticoagulants help keep blood clots from forming in the vessels of people with heart valve conditions and cardiovascular disease. But they don’t do well with NSAIDs, which also have anti-clotting effects. The two together can raise the risk of internal bleeding. Some supplements, including ginseng and vitamin K, have similar blood-thinning qualities and should not be combined with anticoagulants.

Hypertension drugs: NSAIDs, decongestants, weight loss pills, and a smattering of pharmaceuticals can all impact the effects of blood pressure medication in a variety of ways, none of them good. From the natural world, St. John’s wort and grapefruit juice are also best avoided for people on hypertension drugs.

Opioids: These addictive painkillers are deadly enough on their own, accounting for considerably more drug overdose deaths in the U.S. than heroin. Combining them with anti-anxiety meds, sleep aids, alcohol, or muscle relaxants can depress breathing and other vital bodily functions to deadly levels. Morris warns about taking some opioid drugs, including OxyContin and Percocet, with acetaminophen-based painkillers such as Tylenol.

“A lot of people don’t realize that these opioid drugs have a big dose of acetaminophen in them, so if they take Tylenol for a headache, the levels become dangerous to the liver,” she explains.

Statins: Several varieties of medications, including some antibiotics, antidepressants, and HIV drugs, may interfere with the body’s metabolism of the popular cholesterol-reducing statins, leading to muscle aches and soreness. Statins can also react badly with niacin, a B vitamin that also possesses cholesterol-lowing properties. Morris points out that statins are another class of medications that don’t do well with grapefruit juice.

Since there are so many potential adverse drug interactions, the best way to prevent them is to consult your pharmacist and tell your doctor about everything you take.

“Many pharmacies participate in medication management programs,” Morris tells Newsmax Health. “A pharmacist will sit down with a patient and go through records to make sure they have the full picture of the patient’s medications and use of over-the-counter products, and then share that information with the patient’s health care providers.”