Anything with caffeine is bad for the body any time, however unlike other forms of NBE BO doesn't say you have to avoid it to get results because it doesn't rely on water to enlarge the breasts, it causes them to store fat like they do naturally during puberty. However if you're noogling as well then it is bad for the swelling to drink coffee, unless it's decaf.
As far as stevia, one of the many links I got from checking out that diet site I showed you gave me info about it, I can't find the exact link right now. But they said that stevia is 100% natural, there are no chemicals in it like the others. You can actually grow the plant yourself and use fresh leaves from it for seasoning. I know a lot about those artificial sweeteners and won't touch any of them with a 10 foot pole, especially aspartame, it turns to formaldehyde in the blood, which is why a lot of older people who've drank a lot of diet drinks and ate diet foods with it smell funny, like they've been embalmed, cause technically they've been slowly embalming themselves.
Hell, I learned from that link that even splenda (sucralose), which I thought was good because they claim it's made from real sugar is bad because of the chemicals in it. If I can find the link on the artificial sweeteners and stevia I'll attach it so everyone can see it.