The rate of unintentional drug poisoning has skyrocketed in this country mainly due to abuse of prescription drugs that weren’t intended for the user in the first place, according to Wilson Compton, M.D., of the National Institute on Drug Abuse. Too, many people—from teenagers to the elderly—are mixing their own prescription meds with over-the-counter medicines—or worse, illicit drugs or alcohol—with no heed to the warnings about such risks on their prescription bottles. Dangerous medication combinations could put you at risk of everything from car accidents to liver failure and, as in the case of celebrities like Michael Jackson and Heath Ledger, sudden death.

Here are five medication combination that could be fatal:

1. Combining painkillers and sedatives
You’re in pain and you can’t sleep, so you take a prescription painkiller with a prescription sedative. This can be deadly, especially if you take a do-it-yourself approach. Unintentional drug deaths associated with painkillers, especially opiods like OxyContin, Darvon and Demerol, increased 68 percent from 1999 to 2004, according to Dr. Compton. In the majority of cases, opioids were combined with other prescription drugs like tranquilizers (Valium, Xanax) or muscle relaxants. (Often such drugs are combined for the feel-good, mind-numbing effects.) Adding alcohol to the mix raises your risk of death. Other combinations with painkillers, like muscle relaxants or sleeping pills, also can be lethal. Not incidentally, 63 percent of the people who died in the National Institute on Drug Abuse's study did not have a prescription, meaning they got the drugs from their home medicine cabinet, a friend, on the street or some other source.

Prevention: For pain, always choose a pain reliever over a sedative. Only take what’s prescribed to you and do not increase your dose. If you receive two prescriptions from two different doctors, ask your pharmacist if they are safe to take together, and heed warnings not to take any medication with alcohol.

2. Taking too much acetaminophen
Nearly everyone has this painkiller in his or her medicine cabinet (whether as a generic or under a brand name like Tylenol) and it’s safe in appropriate doses. But it can cause serious illness when you take too much. An estimated 56,000 people a year end up in the ER for doing just that, according to the FDA.

Unintentional overdoses, which can cause liver damage or liver failure, happen for several reasons: Some people consider the over-the-counter drug safe and don’t abide by the recommended maximum dose. Others combine two preparations of the drug, like a cold medicine and Tylenol, each containing acetaminophen, and unwittingly doubling their dose. To lower the risk of overdose, an advisory committee recently recommended that the Food and Drug Administration lower the maximum tablet strength to 325 milligrams, and the total daily dose from 4,000 to 3,250 milligrams a day. The committee also recommended taking Percocet and Vicodin off the market. The two drugs contain an opioid and acetaminophen, but experts believe the acetaminophen is often unnecessary and its levels can rise dangerously high when trying to control pain with an opioid.

Prevention: Read your labels carefully—sometimes acetaminophen is called APAP on the prescription bottle—and don’t take more than one medicine containing acetaminophen at a time. Stay within the recommended daily limit of 4,000 milligrams.

3. Combining blood pressure drugs and decongestants
Dad’s blood pressure is now under control with a daily prescription pill. Then he gets a bad cold and starts taking an over-the-counter decongestant that contains pseudoephedrine or phenylephrine. That can cause a dangerous spike in blood pressure and heart rates. “If you’re taking a medicine for a chronic condition and then get a cold once in a while, you don’t always remember what you should be avoiding,” says Sarah Ray, a spokesperson for the American Pharmacists Association.

Prevention: Check with your doctor or pharmacist before adding a new medication to your regimen, and ask what would be the safest decongestant and dosage for you.

4. Combining blood thinners and ibuprofen
Your grandma has a heart condition and also painful arthritis, but popping a pill for both can be dangerous. People with heart conditions who are prescribed “blood thinners” like warfarin (Coumadin) should not take aspirin or a non-steroidal anti-inflammatory like ibuprofen (Advil, Motrin). The combination could cause stomach ulcers or gastrointestinal bleeding. The American Geriatrics Society recently commended that patients age 75 or over not to take non-steroidal anti-inflammatory drugs at all, because of their risks.

Prevention: Aside from ibuprofen, there are a number of drugs, including some antibiotics, that should not be combined with blood thinners. (If they need to be taken, the patient’s blood should be carefully monitored.) If you're taking a blood thinner, check with your doctor for every new drug you take.

5. Mixing ADHD drugs with recreational drugs
Recreational use of attention deficit hyperactivity disorder drugs, such as Adderall, started as a way for high school and college students to enhance their brain power and stay up later studying. According to a new study, abuse of ADHD drugs is on the rise amongst children, and it’s not just the studious who are taking it. Now, “they’re not really being used as study aids as much as they’re being used as part of intoxication at parties,” says Dr. Compton. These stimulant drugs can cause an irregular heartbeat, extreme anxiety and other psychiatric symptoms. The risks vary depending on the person and what they’re combining it with. Combining a stimulant with another stimulant, like cocaine, could very easily lead to an overdose.

Prevention: If your child’s at college, he or she may have access to these drugs from friends. Talk to your child about the risks.