Thalidomide was discovered by accident in 1954 by chemists in Germany who were trying to produce an anti-histamine.

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The immune system produces histamine to fight off the intruder and that chemical causes the symptoms that make people miserable.

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In this phase mast cells - which are responsible for causing allergies - release histamine and other molecules such as chemokines.

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Now entering human trials, it blocks a newly discovered receptor known as H3, the third in a family of crucial cell-surface proteins that receive messages from the hormone histamine.

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