Harmful or toxic reactions to normal doses of common medications are?

The answer is an adverse drug reaction.

 Some reactions to normal doses of common medications are expected and these are known as side effects. But, sometimes organism can react unexpectedly and have harmful or toxic reaction. The adverse drug reaction is an unexpected reaction (harmful or toxic) to normal doses of common medications. It is often due to variations in individual metabolic processes, illness, aging, immunological sensitivities, etc.

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