Some of a drug have a stronger effect than the drug itself.

Some substance of a drug has a stronger effect than the drug itself. There are types and kinds of substances that can cure and can destroy your health conditions if taken without the right prescription of the physician. Many drugs have stronger substances that have strong side effect.

The answer is effect. It is because it fits and completes the statement above as the effect of the drug causes strong or weak effect to a person depending on its dose and the substance that is made of the drug, having an effect to the person using or has ingested it.

Hope I helped