Learn Hardcore Esperanto: Mi mem prenas la medikamenton kvin tagojn en la semajno. - I myself take the medicine five days a week.

Mi prenas la medikamenton = I take the medication.
Mi mem prenas la medikamenton = I myself take the medication (not someone else on my behalf, or not the nurse, etc.).

So mem stresses who is doing the action. It doesn’t change the basic meaning, it just emphasizes the subject (here: mi).

Where can mem go in the sentence, and does its position change the meaning?

Typical and most natural here is:

Mi mem prenas la medikamenton… – emphasizes I (I myself).

Other possibilities and their nuances:

Mi prenas la medikamenton mem… – usually emphasizes la medikamenton: the medication itself (as opposed to something else), or can sometimes mean I take the medicine myself (not having it given), depending on context.
Mi prenas mem la medikamenton… – possible, but less natural; the emphasis is weaker and word order feels a bit odd.

General rule:

Pronoun + mem (e.g. mi mem, li mem) → emphasis on the person.
Noun + mem (e.g. la medikamento mem) → emphasis on the thing itself.

So for the meaning I myself take…, Mi mem prenas… is the best choice.

Why does medikamenton end in -n instead of just medikamento?

The ending -n marks the accusative case, which Esperanto uses mainly for:

Direct objects (the thing directly receiving the action).
Some extra functions like time duration or direction.

Here, la medikamenton is the direct object of prenas (take).
Pattern:

Mi prenas la medikamento ❌ (wrong)
Mi prenas la medikamenton ✅ (correct)

Structure:

Mi – subject (I)
prenas – verb (take)
la medikamenton – direct object (what I take)

So -n is required because the medicine is what is being taken.

Why do we say la medikamenton with la? Could I just say Mi mem prenas medikamenton…?

La is the definite article, like the in English.

la medikamenton = the medication (a specific one already known from context).
medikamenton without la = a medication / some medication (not specifically identified).

If you are talking about a specific prescribed medicine, la medikamenton is natural. If you just mean I take medication (unspecified) five days a week, you could say:

Mi mem prenas medikamenton kvin tagojn en la semajno.

So both are grammatically correct; the choice depends on whether the medicine is specific (la) or not.

Why does kvin tagojn also have -n on tagojn?

Here kvin tagojn is not a direct object; it is an example of the accusative of time duration.

In Esperanto, the accusative -n can mark how long something lasts:

Mi restis du tagojn. – I stayed for two days.
Li laboris tri horojn. – He worked for three hours.

In your sentence:

kvin tagojn = for five days (duration).

So tagojn takes -n because we are expressing the length of time (five-day duration) of the action of taking the medication.

Is kvin tagojn the subject or the object?

Neither.

Subject: Mi (the one who acts).
Direct object: la medikamenton (the thing being taken).
kvin tagojn is an adverbial phrase of time duration (for how long / how many days).

Even though tagojn has -n, it is not the direct object; here the -n is used for duration.

Why do we add en la semajno? Doesn’t kvin tagojn already express time?

Kvin tagojn alone means for five days (stretch of five days).

Mi prenas la medikamenton kvin tagojn. – I take the medication for five days (e.g., from Monday to Friday one time only).

By adding en la semajno (in the week), you indicate a recurring weekly pattern:

Mi mem prenas la medikamenton kvin tagojn en la semajno.
≈ I myself take the medicine five days a week (habitually, every week).

So:

kvin tagojn – duration.
en la semajno – within the span of each week, suggesting a per-week routine.

Is kvin tagojn en la semajno the most natural way to say “five days a week” in Esperanto?

It is understandable and correct, but many speakers would prefer a slightly more idiomatic form, such as:

Mi mem prenas la medikamenton kvin tagojn semajne.
Mi mem prenas la medikamenton semajne kvin tagojn.

Here semajne means per week / weekly.
So:

kvin tagojn en la semajno – literally five days in the week.
kvin tagojn semajne – more compact and often more natural: five days per week.

Both are acceptable, but semajne is very common for this idea.

Could I leave out en la semajno altogether?

Yes, but the meaning changes.

Mi mem prenas la medikamenton kvin tagojn.
Normally means: I myself take the medication for five days (total) – for example, a single five‑day course.

If you want to express a habit, like five days every week, it is better to say:

Mi mem prenas la medikamenton kvin tagojn semajne.
or
Mi mem prenas la medikamenton kvin tagojn en la semajno.

So en la semajno (or semajne) is what makes it clearly “per week” and not just a one‑time five‑day period.

How do I clearly say “for five days in a row” instead of “five days a week”?

To emphasize consecutive days:

Mi mem prenas la medikamenton dum kvin sinsekvaj tagoj.
= I myself take the medicine for five consecutive days.

Key elements:

dum – for (during).
kvin sinsekvaj tagoj – five consecutive days.

For five days a week (repeated habit), stick with:

kvin tagojn semajne
or
kvin tagojn en la semajno.

Why is the verb prenas in the present tense if this is a regular habit?

Esperanto uses the present tense for habitual actions, just like English:

Mi prenas la medikamenton kvin tagojn semajne.
= I take the medicine five days a week. (habitually)

Tenses:

prenas – present (now, general habit, ongoing routine).
prenis – past (I took).
prenos – future (I will take).

So for a regular, current routine, prenas is exactly right.

Does semajno in Esperanto always mean a 7‑day week like in English?

Yes.

Semajno is a normal seven‑day week. There is no special shorter or longer “week” meaning. Days of the week:

lundo, mardo, merkredo, ĵaŭdo, vendredo, sabato, dimanĉo

So kvin tagojn en la semajno will usually be understood as five of those seven days in a typical week.