Usage patterns
〈物〉に効果があるto be effective for something
This medicine is effective for headaches.
効果を発揮するto demonstrate/show an effect
The new fertilizer showed its effectiveness.
効果が現れるfor an effect to appear/show up
The effects appeared after a month of exercising.
効果を期待するto expect/hope for an effect
We are hoping for a big effect from this new policy.
Expressions
効果が上がるtake effect; bear fruit; produce results 効果を上げるhave an effect; be effective; produce a (good) result