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There are major differences in the metabolism of morphine and the illegal drug heroin. Morphine mostly produces its CNS effects through m-receptors, and at k- and d-receptors. Heroin has a slight affinity for opiate receptors. Most of its actions are due to metabolism to active metabolites (6-acetylmorphine, morphine, and morphine-6-glucuronide).
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.
When intravenous medications are involved in adverse drug events, their harmful effects may occur more rapidly, and be more severe than errors with oral medications. This is due to the direct administration into the bloodstream.
Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.
Throughout history, plants containing cardiac steroids have been used as heart drugs and as poisons (e.g., in arrows used in combat), emetics, and diuretics.