Learn Italian: Marco ha finalmente preso la medicina.

It is the irregular past participle of prendere (to take). In the past tense, regular verbs ending in -ere usually change to -uto, but prendere is a very common exception and becomes preso.

Why is finalmente placed right in the middle of the verb ha preso?

In Italian, common adverbs like finalmente (finally), sempre (always), and già (already) are usually sandwiched right between the helper verb (ha) and the past participle (preso).

Why do we use ha instead of è as the helper verb here?

We use a form of avere (ha) because prendere is a verb that acts on a direct object. Marco took something (la medicina). Verbs that answer the question what or who almost always use avere to form the past tense.

Do Italians always use prendere for medicine, just like in English?

Yes! Just like in English, you take a medicine (prendere una medicina) rather than eating or drinking it, even if it is a liquid syrup.