The medicines that sold online can be fake (counterfeit or 'copycat' medicines); can be too strong or too weak, or have dangerous ingredients, or have expired (are out-of-date), or haven't been approved or checked for safety and effectiveness, can be made using non-safe standards, or not safe to use with other medicine or products you use.

You have to talk with your doctor and have a physical exam before you get any new medicine for the first time. Use only medicine that has been prescribed by your doctor or another trusted professional.

Make sure the site requires a prescription and has a pharmacist available for questions.

Buying your medicine online can be easy. Just make sure you do it safely.

If you take several different medicines, see more than one doctor, or have certain health conditions, you and your doctors need to be aware of all the medicines you take. Doing so will help you to avoid potential problems such as drug interactions.

The most important enzymes in the liver that metabolize drugs are called the cytochrome P450 family of enzymes. These enzymes break down drugs when they pass through the liver or small intestine.

It used to be that the only way to test for drug interactions was in people. Now drug companies can take five test tubes with the five major pathways for metabolism and put their drugs in to see whether it's metabolized by CYP450. This allows to generate a list of possible interactions based on their findings.

Over the last several years, there has been a substantial increase in the number of drug-interaction studies the FDA sees in new drug applications. If drug interactions are significant enough, they can prevent a drug from being approved by the FDA. If the agency determines that known drug interactions can be managed and that a drug's benefits outweigh the risks for the intended population, a drug will be approved. Drug-interaction information then goes into the drug's labeling in the sections on "clinical pharmacology," "precautions," "warnings," "contraindications," and "dosage and administration."

The large number of drugs on the market, combined with the common use of multiple medications, makes the risk for drug interactions significant. Consumers need to tell doctors what they're taking and ask questions, and health professionals could do a better job at trying to get the information they want.

Drug interactions with other drugs includes both prescription and over-the-counter medicines. Tricyclic antidepressants such as Elavil (amitriptyline) and Pamelor (nortriptyline) can interfere with blood pressure-lowering Catapres (clonidine). Taking the antibiotic Cipro (ciprofloxacin) with antacids lowers Cipro's effectiveness.

Some antibiotics, such as rifampin, can lower the effectiveness of birth control pills. Sildenafil, the active ingredient in the erectile dysfunction drug Viagra, should not be taken with nitrates for heart treatment because of the potential for dangerously low blood pressure.

Examples of food with tyramine are cheese and soy sauce. Grapefruit juice should not be taken with certain blood pressure-lowering drugs or cyclosporine for the prevention of organ transplant rejection. Alcohol should not be taken with pain relievers such as Tylenol (acetaminophen) or ibuprofen because of the increased risk of liver damage or stomach bleeding.

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