魔弹

[ noun ]
a remedy (drug or therapy or preventive) that cures or prevents a disease
<noun.artifact>
there is no magic bullet against cancer

magic bullet \magic bullet\ n. [From the notion of a bullet that
will kill only the bacterium or disease it is intended for.]
A drug or therapy or preventive that cures or prevents a
disease, with only minimal side effects; as, there is no
magic bullet against cancer.
[WordNet 1.5]