यह दवा ज़हर नहीं है।

Yes—यह can mean this, he, or it depending on context.

In this sentence, यह दवा means this medicine, so यह is working as a demonstrative adjective, like this in English.

A few examples:

• यह दवा = this medicine
• यह आदमी = this man
• यह अच्छा है = this/he/it is good depending on context

Hindi often uses the same word where English uses different words.

Hindi usually follows Subject – Object/Complement – Verb order, while English usually follows Subject – Verb – Complement.

So:

• यह दवा = subject
• ज़हर = complement
• नहीं है = is not

Literally, the structure is closer to:

• This medicine poison not is

That is normal Hindi word order.

दवा means medicine, medication, or remedy.

It is a very common feminine noun in Hindi.

Examples:

• यह दवा अच्छी है। = This medicine is good.
• दवा लो। = Take the medicine.

ज़हर means poison.

The dot under ज़ is called a nukta. It changes the basic letter ज so that it represents a sound closer to z rather than j.

So:

• ज = usually like j in jam
• ज़ = like z in zoo

In everyday writing, some people may write जहर instead of ज़हर, but ज़हर is the more precise spelling.

In Hindi, नहीं usually comes before the verb it negates.

So:

• है = is
• नहीं है = is not

That is why the sentence ends with नहीं है.

More examples:

• वह यहाँ नहीं है। = He/She is not here.
• मैं तैयार नहीं हूँ। = I am not ready.

है is the present-tense form of to be for a singular subject in this kind of sentence. Here it means is.

So:

• यह दवा ज़हर है। = This medicine is poison.
• यह दवा ज़हर नहीं है। = This medicine is not poison.

Hindi often leaves the verb to be until the end of the sentence.

Because यह dवा is singular.

• है = is
• हैं = are / polite is

Since this medicine is one thing, Hindi uses है.

Compare:

• यह दवा ज़हर नहीं है। = This medicine is not poison.
• ये दवाएँ ज़हर नहीं हैं। = These medicines are not poison.

Yes, दवा is feminine.

In this specific sentence, you do not see much effect from that, because:

• ज़हर does not change here
• नहीं does not change
• है is just singular is

But gender matters in many other sentences, especially with adjectives and past participles.

For example:

• यह दवा अच्छी है। = This medicine is good.
  Here अच्छी is feminine to match दवा.

If the noun were masculine:

• यह फल अच्छा है। = This fruit is good.

Hindi does not normally use articles like English a, an, and the.

So दवा can mean:

• medicine
• a medicine
• the medicine

The exact meaning depends on context.

In this sentence, यह already points to a specific thing, so यह दवा naturally means this medicine.

Yes. That would be a slightly different sentence.

Your sentence says:

• यह दवा ज़हर नहीं है।
• literally: This medicine is not poison.

A related sentence would be:

• यह दवा ज़हरीली नहीं है।
• This medicine is not poisonous.

So:

• ज़हर = poison, a noun
• ज़हरीली = poisonous, an adjective

Hindi can express both ideas, just like English.

Learners often see it written as yah or yeh in transliteration, but in modern spoken Hindi it is usually pronounced closer to yeh.

So:

• यह ≈ yeh
• वह ≈ voh

But pronunciation can vary a little by speaker and style.

In everyday speech, many speakers say ये where careful written Hindi uses यह.

So you may hear:

• ये दवा ज़हर नहीं है।

In conversation, that is very common. In standard writing, यह is usually preferred for singular this.

This is one of those places where spoken Hindi is often a bit looser than textbook Hindi.