4 sentences

1. 这种止痛药见效很快。

   zhè zhǒng zhǐ​tòng​yào jiàn​xiào hěn kuài.

   This painkiller works very quickly.

   Source: Dong Chinese Dictionary

2. 这种新药见效很快。

   zhè zhǒng xīn yào jiàn​xiào hěn kuài.

   This new medicine takes effect very quickly.

   Source: Dong Chinese Dictionary

3. 多久才会见效？

   duō​jiǔ cái huì jiàn​xiào?

   How long before it takes effect?

   Source: OpenSubtitles

4. 这种药物需要长期服用才能见效。

   zhè zhǒng yào​wù xū​yào cháng​qī fú​yòng cái néng jiàn​xiào.

   This medication needs to be taken long-term to be effective.

   Source: Dong Chinese Dictionary