That slows the next reaction, a problem because the substance that will become the drug is highly unstable and decomposing, sharply lowering the yield.

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Blocking substance P triggers a molecular chain reaction that boosts levels of the neurotransmitter serotonin, apparently much more selectively than Prozac does.

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An allergic reaction happens when the body identifies a normally harmless substance such as pollen as an invading germ.

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None of these methods, however, says anything about the severity of symptoms that a person will experience if he or she ingests the substance -- for some, there may be no reaction at all.

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