Lees de bijsluiter voordat je pillen inneemt.

Bijsluiter is the information leaflet/package insert that comes with medicine. It is the paper with dosage, warnings, side effects, and instructions.

So in this sentence, it does not mean just any leaflet; it specifically means the leaflet enclosed with the medication.

Lees is the imperative form of lezen (to read). It means Read!

Dutch often uses the imperative in instructions, warnings, and packaging language:

• Lees de bijsluiter.
• Schud voor gebruik.
• Bewaar buiten bereik van kinderen.

A small spelling point: the stem of lezen is lees, not lez, because Dutch doubles the vowel to keep the long ee sound.

Because de bijsluiter refers to a specific leaflet: the one that comes with the medicine.

Pillen here is used in a general sense, like pills/medication as a category, so Dutch often leaves out the article.

Compare:

• Lees de bijsluiter voordat je pillen inneemt. = before taking pills / medication
• Lees de bijsluiter voordat je de pillen inneemt. = before taking the specific pills already being discussed

Both are possible, but the version without de sounds more general.

Use voordat when before is followed by a full clause with a subject and verb.

Here you have:

• je pillen inneemt = you take pills

So Dutch needs voordat:

• voordat je pillen inneemt

Use voor before a noun or noun phrase:

• voor het innemen van pillen = before taking pills
• voor de maaltijd = before the meal

So:

• voordat + clause
• voor + noun phrase

Because voordat introduces a subordinate clause, and in Dutch subordinate clauses, the conjugated verb usually goes to the end.

So:

• main clause: Je neemt pillen in.
• subordinate clause: ... voordat je pillen inneemt.

That is a very common Dutch pattern:

• omdat hij ziek is
• als je tijd hebt
• voordat je pillen inneemt

Innemen is a separable verb.

That means:

• in the infinitive, it is one word: innemen
• in a main clause, it often splits: je neemt pillen in
• in a subordinate clause, it stays together: voordat je pillen inneemt

More examples:

• Ik neem de medicijnen in.
• Hij heeft de medicijnen ingenomen.
• Het is belangrijk om de medicijnen in te nemen.

So the form changes depending on the grammar of the sentence.

Je is the normal unstressed informal form of you.

• je = neutral, common, everyday
• jij = stressed or emphasized you
• u = formal/polite you

In instructions, Dutch often uses je to address the reader in a general, direct way.

Compare:

• voordat je pillen inneemt = before you take pills
• voordat jij pillen inneemt = before you take pills (emphasis)
• voordat u pillen inneemt = formal/polite

Yes. Innemen is a very common verb for taking medicine, especially when following medical instructions.

So:

• pillen innemen
• medicijnen innemen
• tabletten innemen

A related verb is slikken, which means to swallow. That focuses more on the physical act of swallowing:

• Deze pillen moet je met water slikken.

So:

• innemen = take medicine, in the medical/instruction sense
• slikken = swallow

Because it comes from the verb nemen (to take), whose stem is neem.

When combined with in-, you get:

• innemen = to take in / to take (medicine)
• ik neem in
• jij neemt in
• dat je inneemt

The ee stays because the vowel is long. So inneemt is the regular present-tense form built from neem.

Yes.

A more formal version would be:

• Lees de bijsluiter voordat u pillen inneemt.

A slightly more specific medical version might use tabletten or medicatie instead of pillen:

• Lees de bijsluiter voordat u tabletten inneemt.
• Lees de bijsluiter voordat u medicatie inneemt.

But the original sentence is perfectly natural and clear.