yakuzaishi wa kono kusuri no nomikata o setsumeishite kuremashita.

topic particle

Breakdown of yakuzaishi wa kono kusuri no nomikata o setsumeishite kuremashita.

• を: direct object particle
• の: possessive case particle
• この: this

Questions & Answers about yakuzaishi wa kono kusuri no nomikata o setsumeishite kuremashita.

Why is は used after 薬剤師 instead of が?

は marks 薬剤師 as the topic: As for the pharmacist...

In this sentence, the pharmacist is also effectively the subject of the action, but は presents them as the topic of the statement rather than emphasizing who did it.

If you used が instead, it would put more focus on the pharmacist as the one who explained it, as if answering Who explained it?

So:

• 薬剤師は... = speaking about the pharmacist
• 薬剤師が... = emphasizing that the pharmacist is the one who did it

Both can be grammatical, but は is very natural here.

What exactly does この modify?

この modifies 薬.

So:

• この薬 = this medicine
• この薬の飲み方 = how to take this medicine

It does not directly modify 飲み方. The structure is:

• この → 薬
• この薬 → の飲み方

What does の mean in この薬の飲み方?