noun
BAD : Political stability acts as a stimulant for foreign investment.
GOOD : Political stability acts as a stimulus for foreign investment.
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A stimulant is a drug, medicine, etc, which makes the mind or body more active: 'The caffeine in coffee acts as a stimulant.'
When you are not talking about a drug or medicine, use stimulus
(= something which causes activity, growth, or greater effort): 'The new textbook provided a good stimulus for both teachers and students.'