Be/go on the wagon
Definition 1 of 1
Pro Tip 1/3Sobriety Choice
The phrase emphasizes a personal decision to stop drinking for health or personal reasons. 
She chose to be on the wagon before her health got worse.
Pro Tip 2/3Temporariness
Being 'on the wagon' can be a temporary commitment, not always permanent. 
After a month of sobriety, he fell off the wagon at the party.
Pro Tip 3/3Idiomatic Nuance
It's important to note the phrase is informal and often used in casual conversation. 
My uncle has been on the wagon for three years now.