Le médecin dit qu’il faut mâcher ce comprimé au lieu de l’avaler tout de suite.

Because que becomes qu’ before a word that starts with a vowel sound, to make pronunciation smoother. This is called elision.

So:

• que il → qu’il

You will see this very often in French:

• qu’il
• qu’elle
• qu’on

In this sentence, Le médecin dit qu’il faut... means The doctor says that it is necessary to...

Il faut is a very common French expression meaning:

• it is necessary
• one must
• you have to / it is necessary to, depending on context

The verb is falloir, which is mostly used only in the form il faut in everyday French.

The il here does not mean a specific he. It is an impersonal il, like the it in English it is necessary or it is raining.

So:

• il faut mâcher ce comprimé = it is necessary to chew this tablet
• more natural English: you need to chew this tablet

They are infinitives because they follow structures that require the infinitive:

1. il faut + infinitive

   • il faut mâcher = it is necessary to chew

2. au lieu de + infinitive

   • au lieu de l’avaler = instead of swallowing it

So French keeps both actions in their base verb form:

• mâcher = to chew
• avaler = to swallow

Au lieu de means instead of.

It is followed by:

• a noun, or
• an infinitive verb

In this sentence:

• au lieu de l’avaler = instead of swallowing it

Examples:

• Au lieu de partir, il reste. = Instead of leaving, he stays.
• Au lieu du café, je prends du thé. = Instead of coffee, I’m having tea.

So here, the doctor is contrasting two actions:

• mâcher the tablet
• not l’avaler tout de suite

The l’ is a direct object pronoun meaning it. It stands for ce comprimé.

So instead of repeating the noun, French uses a pronoun:

• au lieu d’avaler ce comprimé
• au lieu de l’avaler

Both are possible, but using the pronoun avoids repetition and sounds natural.

It becomes l’ instead of le because avaler starts with a vowel:

• le avaler → l’avaler

So:

• l’ = it
• de l’avaler = of swallowing it / more naturally, instead of swallowing it

French has different forms of this / that before masculine singular nouns:

• ce before most consonant sounds
• cet before a vowel sound or silent h
• cette for feminine singular nouns

Since comprimé starts with the consonant sound k, you use ce:

• ce comprimé

Compare:

• ce livre = this book
• cet hôpital = this hospital
• cet avocat = this lawyer / this avocado
• cette tablette = this tablet

Yes. Un comprimé is a tablet or pill, especially in a medical context.

It is a masculine noun:

• le comprimé
• ce comprimé

A learner might also come across:

• une pilule = a pill
• un médicament = a medicine / medication

But comprimé is a precise and very common word for a tablet.

• mâcher = to chew
• avaler = to swallow

In this sentence, the contrast matters medically:

• il faut mâcher ce comprimé = you need to chew the tablet
• au lieu de l’avaler = instead of swallowing it whole

So the sentence implies that this medicine is meant to be chewed first, not swallowed immediately.

Tout de suite means right away, immediately, or straight away.

So:

• l’avaler tout de suite = to swallow it right away

It often has the sense of doing something without waiting.

Examples:

• Je reviens tout de suite. = I’ll be right back.
• Fais-le tout de suite. = Do it right away.

In this sentence, it suggests:

• do not swallow it immediately
• chew it first

In French, object pronouns usually come before the verb they belong to.

So:

• avaler le comprimé = to swallow the tablet
• l’avaler = to swallow it

This is normal French word order with pronouns.

Other examples:

• voir le médecin → le voir = to see him / it
• manger la pomme → la manger = to eat it

Even when the verb is an infinitive, the pronoun still usually goes before it:

• de l’avaler
• pour le faire
• sans la prendre

Yes, that would be possible, but it is slightly different in tone.

• il faut mâcher ce comprimé = it is necessary to chew this tablet
• on doit mâcher ce comprimé = we/you/people must chew this tablet

Il faut sounds more impersonal and general, which is very common for instructions, rules, and advice.

A doctor, label, or instruction often uses il faut because it sounds like a general requirement.

Mâcher is pronounced roughly like mah-shay.

The â does not usually change the meaning by itself here in a way you need to worry about first; it mainly reflects spelling/history and can affect pronunciation slightly depending on accent. The important thing for learners is:

• mâcher sounds like mah-shay
• the -er ending is pronounced -ay

So:

• mâcher
• avaler
• parler

all have that common infinitive ending sound.

Because the subject is Le médecin, which is he/she in meaning, so the verb dire must be in the third person singular:

• je dis = I say
• tu dis = you say
• il/elle dit = he/she says

So:

• Le médecin dit... = The doctor says...

Even though médecin is a noun and not a pronoun, it still takes the same verb form as il/elle because it is singular.

Yes, it is completely natural. It means The doctor says that...

French often uses:

• dire que = to say that

So:

• Le médecin dit qu’il faut... = The doctor says that you need to...

In real life, French could also use:

• Le médecin a dit qu’il fallait... = The doctor said that it was necessary to...
• Le médecin recommande de... = The doctor recommends...
• Il faut... on its own for instructions

But the sentence you have is very standard and natural.

Yes. If the tablet has already been identified, French could say:

• Il faut le mâcher au lieu de l’avaler tout de suite.

Here:

• le mâcher = to chew it
• l’avaler = to swallow it

That is grammatically correct and natural when the object is already known from context. The original sentence keeps ce comprimé explicit, which is especially helpful in instructions.