Alcohol and drugs affect everyone differently. While they're generally viewed as leisure activities, some people get extra motivated when under the influence. Take advantage of this phenomenon by creating a to-do list before you imbibe.
Part of the effects of cannabis and alcohol is that our bodies start to run on automatic while our senses and decision making skills slow down (a dramatic over-simplification, but bear with me). This means we'd be pretty bad at driving or performing surgery, but doing the dishes, working out, sketching out ideas, or even writing can all be boosted by this altered state. Provided you're not too far gone, of course. Why not make the most of it and write down what you'd like to get done?
Of course, not everyone works the same way and some people will immediately lose motivation when they're in an altered state. As one reddit user points out, if indulging your habits saps your motivation, you can try the opposite approach: create a to-do list of things to get done before you partake. That way, instead of feeling guilty about that whiskey and ginger ale (shut up, it's delicious) at the end of the day, you're sitting on a field of victory enjoying a few well-earned comforts.