Several websites include the following sentence as one of the exercises in the use of PARTICIPLES and each one gives RELIEVING as the correct answer.

However, a friend of mine who has been in the US for more than 20 years claim that RELIEVING is wrong and is never used by Americans. He said the answer should have been A RELIEF.

May I know your stand on this? Again, all my thanks.

Keliher said it was (relieve) ___ to use marijuana legally after thirty years of being a "closet marijuana smoker."
Yes, 'a relief' is my natural reaction, but 'relieving' is not wrong; it is simply less common.
Thank you so much, Mister Micawber.