But when a person is in shock, their organ walls become more permeable, letting harmful substances in and out more indiscriminately, researchers say.

BBC: News

It was blue-sky research, but their idea was that harmful substances should be produced where they are needed, instead of being shipped in bulk from chemical factories.

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The hope is that they will develop a broad aversion to harmful substances that will stay with them through their late teens and early 20s, when drug use peaks.

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The same goes for gin or aspirin, of course: but many voters reasonably wonder whether it would be right to add to the list of harmful substances that are legally available.

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The UK, she said, had taken the lead internationally in developing early warning systems to detect harmful new substances, with drugs able to be banned days after identification under the system of temporary class drug orders.

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These substances are harmful to human health and local air quality.

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There are no hard data on how prevalent such substances are, or how harmful.

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"This is very useful for the understanding of the mechanisms through which smoking induces arterial dysfunction and subsequent cardiovascular disease and hopeful for the discovery of substances capable of reversing smokes harmful effects, " they said.

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