Learn Hardcore German: Diese Salbe ist wirksam gegen Schmerzen. - This ointment is effective against pain.

wirksam means “effective” in the sense of producing the intended effect (here: pain relief). effektiv is a near-synonym, but in medical/product claims wirksam is the go-to word. effizient means “efficient” (good cost/time-to-benefit ratio) and is not appropriate here.

Why is the preposition gegen used, and which case does it take?

gegen (against) is the standard preposition when something combats a symptom or condition. It always takes the accusative. Hence: gegen Schmerzen (accusative plural). With an article: gegen den Schmerz (sing.), gegen die Schmerzen (pl.), gegen meine Schmerzen.

Why is Schmerzen plural here?

German commonly uses the plural for physical pain, especially with symptoms (e.g., Kopfschmerzen, Bauchschmerzen). Singular der Schmerz tends to mean one specific pain or a more abstract/emotional pain. For general claims about products, plural Schmerzen is standard.

Why is there no article before Schmerzen?

German often omits the article with indefinite plural nouns used generically. gegen Schmerzen = “against pain in general.” Add an article when you mean specific pains: gegen die Schmerzen (“against those particular pains”).

Could I use für or bei instead of gegen?

für sounds wrong in this context; German says wirksam/helfen/wirken gegen a symptom.
bei is possible with certain verbs: hilft bei Schmerzen (“helps when you have pain”). You also see wirksam bei in some contexts (“effective in cases of …”), but for fighting symptoms, wirksam gegen is the most idiomatic.

Is the word order fixed? Can I move gegen Schmerzen?

You can move it:

Diese Salbe ist wirksam gegen Schmerzen. (neutral)
Diese Salbe ist gegen Schmerzen wirksam. (slightly more emphatic)
Gegen Schmerzen ist diese Salbe wirksam. (fronts the topic/contrast)

Why is it diese Salbe and not dieser/dieses?

Salbe is feminine (die Salbe). In the nominative singular, the demonstrative is diese. Quick reminder: masculine dieser, feminine diese, neuter dieses, plural diese.

Why doesn’t wirksam have an ending here?

After sein, adjectives are used predicatively and don’t take endings: ist wirksam. If the adjective stands before the noun (attributive), it inflects: eine wirksame Salbe, die wirksame Salbe, wirksame Salben.

Can I use the verb wirken instead?

Yes: Diese Salbe wirkt gegen Schmerzen. Meaning is practically the same. ist wirksam reads a bit more formal; wirkt is very common and natural.

Can I say hilft here?

Yes. Diese Salbe hilft gegen Schmerzen (combats them) or … hilft bei Schmerzen (is helpful when you have pain). Both are idiomatic with a slight nuance in focus.

Are there more specific alternatives to wirksam?

Common choices include schmerzlindernd (pain-relieving), schmerzstillend (pain-suppressing), and the technical analgetisch. Example: Diese Salbe wirkt schmerzlindernd.

How do I pronounce the key words?

Diese: [ˈdiːzə]
Salbe: [ˈzalbə] (initial s like English z)
wirksam: [ˈvɪʁksaːm] (w = v; r is uvular)
gegen: [ˈɡeːɡən]
Schmerzen: [ˈʃmɛʁtsən] (sch = sh; z = ts)

Can I use the singular Schmerz instead of Schmerzen?

Grammatically yes, but it changes the feel. Use singular for a specific pain: … gegen den Schmerz im Knie. For general, non-specific statements about effectiveness, stick with plural Schmerzen.

How do I compare or negate wirksam?

Comparative/superlative: wirksamer, am wirksamsten (e.g., Das ist die wirksamste Salbe gegen Schmerzen.)
Negation: nicht wirksam or the single word unwirksam (e.g., Diese Salbe ist unwirksam gegen Schmerzen.)

Is Salbe the same as Creme?

Not quite. Salbe (ointment) is oil-based and greasier/occlusive; Creme (cream) contains more water and is lighter. The distinction matters in medical and cosmetic contexts.