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Which of these three people is doing something risky?
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Is it the one who takes their cholesterol medication with grapefruit juice?
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The one who takes Acetaminophen pain relievers
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for a sore ankle before going out for drinks?
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Or the one who's on a blood-thinning medication
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and takes an aspirin for a headache?
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Actually, all of them are.
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Each has inadvertently created a drug interaction that could, in extreme cases,
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lead to kidney failure; liver damage;
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or internal bleeding.
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Drug interactions happen
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when the combination of a drug with another substance
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causes different effects than either would individually.
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Foods, herbal supplements, legal drugs, and illicit substances
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can all cause drug interactions.
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Most drug interactions fall into two categories.
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Some take place when two substances' effects influence each other directly.
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In other cases, once substance effects how the body processes another,
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like how it is absorbed, metabolized, or transported around the body.
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Blood thinners and aspirin, for example,
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have similar effects that become dangerous when combined.
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Both prevent blood clots from forming—
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blood thinners by preventing the formation of the clotting factors
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that hold clots together,
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and aspirin by preventing blood cells from clumping into groups
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that become clots.
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Individually, these effects are usually safe,
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but taken together, they can prevent blood clotting to a dangerous extent,
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possibly causing internal bleeding.
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While blood thinners and aspirin are generally harmless
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when taken individually,
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interactions where one substance exacerbates the effects of another
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can also take place between drugs that are independently harmful.
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Cocaine and heroin are each dangerous,
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and those dangers compound when the two drugs are combined—
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even though their behavioral effects may feel like they cancel each other out.
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Cocaine is a stimulant, and many of its effects, like increased heart rate,
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cause the body to need more oxygen.
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But heroin, a depressant, slows breathing—
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reducing the body's oxygen supply just when it needs more.
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This combination strains the organs and can cause respiratory failure and death.
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The interaction between grapefruit juice and certain medications
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in class of cholesterol-lowering drugs called statins,
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has to do with drug metabolism.
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The liver produces enzymes, molecules that facilitate the breakdown of substances
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that enter the body.
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Enzymes can both activate drugs,
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by breaking them down into their therapeutic ingredients
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from more complex molecules, and deactivate them,
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by breaking harmful compounds down into harmless metabolites.
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There are many, many different enzymes,
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each of which has a binding site that fits a specific molecule.
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Grapefruit binds to the same enzyme as statins,
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making less of that enzyme available to break down statins.
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So combining the two means that a greater concentration of the drug
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stays in the bloodstream for a longer period of time,
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potentially causing kidney failure.
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Alcohol can also alter the function of the enzyme that breaks down Acetaminophen,
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the active ingredient in pain relievers like Tylenol and paracetamol.
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When someone takes Acetaminophen, some of it is converted into a toxic substance.
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At the recommended dose,
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there isn't usually enough of this toxic byproduct to cause harm.
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But heavy drinking can alter enzyme activity
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so more of that byproduct is produced,
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potentially causing liver damage
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even with what's usually a safe dose of acetominophen.
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Meanwhile, the herbal remedy Saint John's Wort increases the liver's production
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of a particular enzyme.
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That means the drugs this enzyme is responsible for breaking down
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get metabolized faster—
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sometimes too fast, before they can have their therapeutic effects.
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In spite of the dizzying number of possible interactions,
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most of the dangerous interactions with commonly used drugs are well known.
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And new developments in science are helping us keep better track
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of drug interactions than ever.
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Some researchers are developing AI programs that can predict the side effects
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of drug interactions before they occur,
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using information about the landscape of protein interactions within your body.
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For the new drugs that are being developed all the time,
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supercomputers are being used to find potential interactions
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while those drugs are still in development.