Newton spoke about the challenge Thursday on The Late Late Show with James Corden. The three-time Pro Bowl selection and 2015 NFL MVP said he has a challenge every month.
Newton said in January he committed to not placing bets. He decided to go vegan in February.
"In March ... I hope this is an adult crowd. It looks like it is -- no climax," Newton said. "I'm going through a transition right now. I wanted it to be challenging."
Newton is coming off January shoulder surgery. The eight-year veteran completed a career-high 67.9 percent of his passes for 3,395 yards, 24 touchdowns and 13 interceptions in 14 starts last season. Newton, 29, also ran for 488 yards and four scores for the Panthers in 2018.
The Panthers don't plan to sign a back-up quarterback this off-season as Newton is expected to be ready for Week 1.
"For me, doing certain things to challenge me in the off-season that I can't necessarily do," Newton said. "So now when the season comes around, it makes my mind stronger. I feel like if I go back and I say I did those things, then I'm mentally stronger."
Newton has been posting flowers on social media to signify his monthly challenges. He posted another flower Thursday on his Instagram story and also wrote 21-of-31, signifying how many days he has completed in his March challenge.
The No. 1 pick in the 2011 NFL Draft signed a five-year, $103 million contract extension with the Panthers in 2015.