La medicina redujo el dolor.

Because medicina is a feminine singular noun, and Spanish often uses an article where English might not.

In this sentence, la medicina usually means:

• the medicine (a specific medicine already understood from context), or
• sometimes medicine as a general thing that produced the effect.

The article la agrees with the noun’s grammatical gender: la medicina.

In this sentence, it most naturally means a medicine / medication, not the field of medicine.

So La medicina redujo el dolor sounds like a medicine, treatment, or remedy reduced the pain.

If you wanted to be more explicitly clinical, you might also hear:

• el medicamento = the medication / drug
• la medicación = the medication regimen / medication being taken

But la medicina is very normal in everyday Spanish.

Redujo is the preterite tense, third person singular, from reducir.

That means it refers to a completed action in the past:

• la medicina redujo = the medicine reduced

So the sentence presents the pain reduction as a finished event.

Because reducir has an irregular preterite form.

The preterite of reducir is:

• yo reduje
• tú redujiste
• él/ella/usted redujo
• nosotros redujimos
• vosotros redujisteis
• ellos/ellas/ustedes redujeron

The c changes to j in these forms. This is a spelling change that also keeps the correct sound.

Spanish often uses the definite article with nouns like pain, especially when referring to a specific pain that is already understood from the context.

So el dolor here means the pain—the pain the person had.

Saying just dolor is possible in some contexts, but in this sentence el dolor sounds much more natural.

Because el dolor is a direct object, but it is not a person.

The so-called personal a is mainly used before specific people (and sometimes pets or personified beings), for example:

• Veo a María.

But here:

• La medicina redujo el dolor.

El dolor is a thing/concept, so there is no personal a.

The parts are:

• La medicina = subject
• redujo = verb
• el dolor = direct object

So the structure is the very common subject + verb + object pattern:

• La medicina → did the action
• redujo → the action
• el dolor → what was affected by the action

Yes, Spanish word order is more flexible than English, but La medicina redujo el dolor is the most neutral and natural order.

You might change the order for emphasis, but that would usually sound more marked. For a learner, the standard version is the best one to use:

• La medicina redujo el dolor.

It is clear, natural, and straightforward.

In most of Spain, redujo is pronounced approximately like reh-DU-ho, with:

• j = a strong throaty sound, like the j in jamón
• stress on du
• the r in re- is a soft tapped r

And medicina in most of Spain is approximately meh-dee-THEE-na, because c before i is usually pronounced like the th in thin in most peninsular Spanish.

Both are past forms, but they do not mean exactly the same thing.

• redujo = preterite → a completed action
• reducía = imperfect → an ongoing, repeated, or background action in the past

So:

• La medicina redujo el dolor.
  = the medicine reduced the pain (completed event)

• La medicina reducía el dolor.
  = the medicine was reducing the pain / used to reduce the pain

In your sentence, redujo is used because the reduction is presented as a finished result.