US federal drug regulators on Wednesday required manufacturers to warn against the mental health dangers, including suicidal thoughts, of two popular anti-smoking drugs.

The Food and Drug Administration (FDA) ordered Pfizer, which makes Chantix, and GlaxoSmithKline, maker of Zyban, to place a warning highlighting the "risk of serious mental health events" when taking the drugs, including behavior changes, depression, hostility and suicidal thoughts.

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