causative

Yes, but why would you? It would be a very awkward sentence.

He was helped to carry his boxes by me.

cho7712 I help him carry his boxes.Can that sentence be passivized (as in 'He was helped to carry his boxes.') without no change in meaning?

The two sentences are different in tense; therefore there is a change in meaning.

Note that 'help' is not a causative verb.

Thank you all for the answers.
Does 'awkward' mean grammatical despite of the unnaturalness?
And it was my mistake to use the past tense.
'Help' is taught to belong to the causative verb here in Korea.
Could you let me know where I can find more about what you said?

Yes, awkward means it's both grammatical and unnatural.

Many, many exercises with the passive result in horrible sentences no native speaker would ever produce naturally.
I think one of my favorites was "Soccer was played all day by me."

Note: If you wanted it in the present tense, then:

He is being helped to carry his boxes by me.

But, again, the direct is better than the passive.