A médica disse que esta vitamina pode ajudar quando estou muito cansado.

to be

Breakdown of A médica disse que esta vitamina pode ajudar quando estou muito cansado.

• cansado: tired
• esta: this
• muito: very

Questions & Answers about A médica disse que esta vitamina pode ajudar quando estou muito cansado.

Why is it “A médica” and not just “médica” or “uma médica”?

In European Portuguese, the definite article (o, a, os, as) is used much more than in English.

• A médica = the doctor (female) → we assume the speaker and listener know which doctor they’re talking about (e.g. my doctor, the doctor from the clinic, etc.).
• Uma médica = a (female) doctor → introduces a doctor not yet identified/specified.
• Bare “médica disse…” (without an article) is not natural here in European Portuguese.

So “A médica disse…” implies a specific, known doctor, which is usually what you mean in this kind of sentence.

Why is it “médica” (feminine) and “cansado” (masculine) in the same sentence? Shouldn’t they match?

They agree with different nouns:

• médica agrees with the implied noun a mulher / a senhora (the woman / the lady) → a médica = female doctor.
• cansado agrees with the subject eu (I).

So if I am male:

• estou muito cansado → I (male) am very tired.

If the speaker is female, it should be:

• A médica disse que esta vitamina pode ajudar quando estou muito cansada.

The adjective cansado/cansada always agrees with the person who is tired, not with médica.