We usually think of grapefruit as a food that's good for us. And generally, it is. But before cutting into one, you should check the label on any medications you're taking. That's because grapefruit-and other foods-may interfere with your drugs' effectiveness.

Grapefruit contains chemicals that can prevent certain drugs from breaking down properly. As a result, elevated levels of the medicines may stay in your body longer than intended, leading to side effects.

Other examples include aged cheese, soy sauce and cured meats. These don't mix with antidepressants because they contain high levels of a substance called tyramine. The combination can lead to a dangerous spike in blood pressure.

Other foods can make drugs less effective. Milk can reduce the infection-fighting effects of some antibiotics. Black licorice can interfere with some blood clotting drugs.

Pectin-which is used as a stabilizer in foods like jam-can limit the absorption of the painkiller acetaminophen. And green, leafy vegetables can pose problems if you're on the blood thinner warfarin.

And pay attention to your timing. With some drugs, you should completely steer clear of the food in question. While in other cases, you just need to avoid the food around the time you take the meds.

Yet another reason why it's so important to read the information that comes with your medication before you start taking it.

As always, if you have any questions, ask your doctor or pharmacist.