止痛药 in English:

If you have pain, take a painkiller.

Please give me a painkiller.

I need a painkiller.

She took some painkillers for her headache.

Take some painkillers and go to bed.

After the operation you will need to take painkillers for a few days.

You should take some painkillers for your headache.

This is a strong painkiller and you've already taken 2.

Good painkiller is better than regular booze.

I'm out of painkiller. I've gotta get some.

These painkillers are only available on prescription.