@Selena do you use tobacco to smoke weed?
I have never felt a drop in supply and I’ve smoked thru all 3 of my breastfeeding journeys the first going over 2 years the second over a year and now I’m 9 months in with the third
I smoke backwood blunts for the most part
My suggestion is keep pumping, or latching to keep the supply up. I also drink coconut water, oat milk, and body armor on a daily basis. I smoke daily to add and answering your question it does decrease and for that reason it’s best to keep yourself hydrated