Although not recommend, how does marijuana and smoking marijuana affect breastmilk and the baby? like what does it do?

Could be trouble: Marijuana is legal in my state, but doesn't mean it is safe for all. Evidence emerging that younger children develop cognitive limitations due to usage, and a baby would be at highest risk. Since some are vulnerable to significant psychological and cognitive disabilities, best you avoid marijuana if breast feeding.

Stays a long time: The half life of cannabis in breast milk ranges 25-57hrs depending on the study. There are conflicting outcome studies, some show little developmental impact some show delay.The only clear negative is reduced head size by a year. Smoking by itself increases crib death rate & frequency of respiratory & ear infections by 2-3x even when not done while kid is present.