(idiomatic) Abstaining from drinking any alcoholic drink, usually in the sense of having given it up (as opposed to never having partaken); teetotal.
(by extension) Maintaining a program of self-improvement or abstinence from some other undesirable habit.
He’s been on the smoking cessation wagon for two weeks now.
Used other than figuratively or idiomatically: see on, the, wagon.
Source: en.wiktionary.orgOn the wagon sped, and I, as well as my comrades, gave a despairing farewell glance at freedom as we came in sight of the long stone buildings. Nellie Bly
Here's to five miserable months on the wagon and the irreparable harm that it's caused me. Stanley Kubrick
But then it ceases the day I get back on the wagon and avoid sugar and grains. Source: Internet
Geoffrey was dumped within a year, being unsuitable long-term material: ten years older and very much on the wagon. Source: Internet
This kit was a very nice introduction to Paula's Choice and I'm happy to say that I'll stay on the wagon! Source: Internet
I jumped on the wagon yesterday as part of my training for a half-marathon Mother's Day weekend. Source: Internet