When does placenta take over

[S0987]

So here's what's confusing me:

www.newscientist.com/article/dn27460-womb-milk-nourishes-human-embryo-during-first-weeks-of-pregnancy/amp/

This article basically says the placenta doesn't take over until 11 weeks and until then baby is nourished by womb milk. I'm confused because if that's the case why are we told not to consume or do certain things during early pregnancy for want of protecting baby? I'm not saying let's all go drink and smoke it for the first trimester (I literally am the person who made myself vomit because I accidentally consumed a cherry seed and read that it's poisonous) I am just confused by this if you know what I mean?

Thanks

@Kroot I understand that maternal alcohol is transferred to fetus I'm not disputing that what we are trying to figure out is if it is during early pregnancy when the placenta hasn't formed