i drink daily 6 to 8 cup of milk-tea with suger, any side effect?!

High in sugar, calories and caffeine, may cause weight gaining, diabetic, loss of sleep or stomach upset & teeth staining.
I don't think there is any immediate side effect except the caffeine if you are sensitive.

Please note that an imbalance in the blood sugar level could cause glaucoma, hypertension, anxiety, elevated triglycerides, and kidney diseases. A diabetic could find performing even day-to-day activities very difficult. Sugar also affects the immune system as it may cause a lower number of white blood cells that are needed to fight disease causing bacteria. This is a chronic condition and hence has to be handled carefully.
Excess sugar causes the levels of bad cholesterol to be high while lowering that of the healthy constituent.
Consuming too much sugar can also cause weakness and fatigue too.
So preferred if you could drink without sugar if you are drinking that many cups a day, not forgetting there is already sugar in milk.

Weight gain, diabetes, hyper active...that's a lot for one day.