i yageul saryeomyeon cheobangjeoni piryohaeyo.

사려면 comes from the verb 사다 (to buy) plus the grammar pattern -(으)려면.

So:

• 사다 = to buy
• 사려면 = if you want to buy, if you’re going to buy, or to buy

In this sentence, it gives the idea of a condition or requirement:

• 이 약을 사려면... = if you want to buy this medicine... / to buy this medicine...

A very natural full translation is:

• To buy this medicine, you need a prescription.

을 is the object marker.

• 약 = medicine
• 약을 = medicine + object marker

It marks 약 as the thing being bought.

So in:

• 이 약을 사려면

the object of 사다 (to buy) is 이 약 (this medicine).

English does not use a separate particle like this, so this can feel unusual at first.

이 약 means this medicine.

• 이 = this
• 약 = medicine

So:

• 이 약 = this medicine
• 이 약을 = this medicine (as the object)

The demonstrative 이 is used for something close to the speaker, similar to this in English.

처방전 means prescription.

More specifically, it is the prescription issued by a doctor for medicine.

So:

• 처방전이 필요해요 = a prescription is necessary / you need a prescription

In everyday English, we usually just say prescription, even though the Korean word can feel a little more like prescription slip/form.

Here, 이 is the subject marker.

• 처방전 = prescription
• 처방전이 = the prescription + subject marker

In this sentence, the thing that is necessary is the prescription.

So the structure is basically:

• 처방전이 필요해요
• A prescription is necessary

This is different from English, where we usually say:

• You need a prescription

But Korean often expresses this as:

• A prescription is needed/necessary

필요해요 means is necessary, is needed, or need depending on the translation.

It comes from 필요하다, which means to be necessary.

So:

• 처방전이 필요해요 literally = A prescription is necessary
• natural English = You need a prescription

This is a very common expression in Korean:

• 시간이 필요해요 = I need time / Time is needed
• 돈이 필요해요 = I need money / Money is needed

Korean often omits the subject when it is understood from context.

In English, we usually say:

• You need a prescription to buy this medicine.

But in Korean, it is normal to leave out you if it is obvious.

So:

• 이 약을 사려면 처방전이 필요해요.

naturally implies something like:

• If you want to buy this medicine, you need a prescription.

The sentence does not need 당신은 or another word for you.

Here is the breakdown:

• 이 = this
• 약을 = medicine + object marker
• 사려면 = if you want to buy / to buy
• 처방전이 = prescription + subject marker
• 필요해요 = is necessary / is needed

So the literal order is roughly:

• This medicine, to buy, prescription is necessary.

A natural English version is:

• You need a prescription to buy this medicine.

This is a good example of how Korean word order can differ a lot from English, even when the meaning is straightforward.

This is a very common question.

• 사면 = if you buy
• 사려면 = if you want to buy / if you’re going to buy

So:

• 이 약을 사면... = if you buy this medicine...
• 이 약을 사려면... = if you want to buy this medicine...

In this sentence, 사려면 is better because the meaning is about a requirement before buying the medicine.

So the idea is:

• If you want to buy it, you need a prescription first.

Sometimes, yes. In casual spoken Korean, object particles like 을/를 are often dropped.

So you may hear:

• 이 약 사려면 처방전이 필요해요.

This is still understandable and natural in conversation.

However, the full form:

• 이 약을 사려면 처방전이 필요해요.

is clearer and is a good form for learners to study.

Yes. 필요해요 is in the 해요-style, which is polite and very common in everyday conversation.

So this sentence is polite but not extremely formal.

Compare:

• 필요해요 = polite, everyday standard
• 필요합니다 = more formal
• 필요해 = casual, informal

So you might hear:

• 이 약을 사려면 처방전이 필요합니다.
  This sounds more formal, such as in a hospital, pharmacy notice, or official explanation.

Yes, absolutely.

That is actually one of the best English translations.

Possible natural translations include:

• You need a prescription to buy this medicine.
• A prescription is required to buy this medicine.
• To buy this medicine, you need a prescription.

All of these match the Korean sentence well.

Yes. This pattern is very common.

The structure:

• X-(으)려면 Y이/가 필요해요
• If you want to do X, Y is necessary

is a very useful pattern.

For example:

• 한국에 가려면 비자가 필요해요.
  You need a visa to go to Korea.

• 운전하려면 면허가 필요해요.
  You need a license to drive.

So your sentence follows a very common and practical Korean pattern.