Hmm. Am I the first one to take this course without cheating by looking up the translations here and, therefore, using my own words?
'this medication relieves the pain' should be accepted, I think. https://en.wiktionary.org/wiki/relieve - one of the meanings is 'to alleviate', which is (https://en.wiktionary.org/wiki/alleviate) is to 'make less severe, as a pain or difficulty '.
Maybe there are specific words in Polish for those synonyms, but, sadly, wiktionary does not list them.