I have a friend who drinks 3 diet coke in a day ...

yes it can cause problems my step mother had to stop because she had got addicted to it and it gave her problems in her wrist

What about caffeine effects.

Yes, some diet drinks contain caffeine, and too much caffeine is not healthy for you, it can cause certain minerals and vitamins to not be able to absorb throughout the body.

Just because it doesn't have calories doesn't mean it's good for you and just because something has calories doesn't mean it's bad.  Calories are the a measurement for how much heat your body is able to produce by burning it off.

There's nothing wrong with drinking soda as long as you're also drinking water for that hydration your body desperately needs and getting the correct amount of vitamins and minerals in a day.  If you're worried about your friend overdosing on caffeine, then no, that is not going to happen from only 3 sodas a day.

However, if your question pertains to him saying that he thinks he'll lose weight from drinking a diet soda then the answer is no.  Even if something doesn't have calories in it that doesn't mean that it doesn't have anything in it that will turn into fat. Those labels are tricky. Also, the slight reduction in calorie isn't worth the reduction in taste or the risk of cancer from high levels of fake sugar.  May as well go for the real thing and savor it, then be healthier with other choices. 

There have been so many studies regarding the side effects of diet cola. Like almost everything else we consume, if it is done within moderation, he should be all right. Having said that, all of us are different, and what is considered okay for your friend (3 a day) might be harmful for someone else. I for instance have had Type 1 diabetes for close to 30 years, and also have to eat a gluten-free diet. One of the few things I enjoy in life are diet free soft drinks, but I limit myself to have 1 can a day. In addition, as we all know, if we wait long enough, a new study will come out contradicting the findings of a previous study that we were led to believe was the "holy truth." My advice: enjoy life as best as possible. 

does he sleep good at nite?

does he GLOW in the dark?

does he use the facilities a bit too often?

THREE drinks will not HARM him!!!

I agree with twincitiesmark.  I think it's best to go with the real sugar than the artificial sweeteners, but in moderation.  For one thing, it just tastes better!

Of course it does! lol its soda and any kind of soda can mees up your poor kidneys . My cousin used to drink soda everyday for 14 years, almost her whole life, then she had a dream. In the dream her grandmother was telling her that one day that soda was gonna kill her. So She went to the doctor, and sure enough it was destroying her kidneys. So she stopped. Just tell your friend to be careful and don't drink too much. ( my cousin was 16 when she went to her doctor )