If I start taking creatine, will I have to keep on taking in order to work out at the same high intensity? Will my body become reliant on it? What are the negative effects of artificially (or naturally I dont know) enhancing your levels of ATP? Or negative effects on the body in general?
Creatine supplementation does suppress the body's synthetic production of creatine (done in the kidneys). There are a couple of different theories on dosing and cycling the supplement and plenty of info on the web, some of it reliable. When you stop taking creatine the supplement effect declines over a period of 3-4 weeks and creatine concentration returns to natural levels over that time.
Creatine doesn't increase peak power in a single movement/exercise but (because supplementing creatine speeds ATP replenishment) it does improve performance in successive repetitions of high-intensity effort done following short recovery intervals so the ultimate benefit is more time spent at higher intensity. If the high-intensity efforts are dependent on creatine supplementation then yes, intake must be maintained to keep achieving the same output until the body adapts structurally or functionally to the new level of effort.
Creatine supplements may increasing cramping and muscle soreness (studies not clear). Creatine may compromise aerobic and endurance performance, either due to weight gain associated with taking it or increased fluid retention that makes the heart work harder to circulate. Creatine has been associated with heart attacks in athletes who would not otherwise be susceptible (again, studies not clear). This may have something to do with fluid retention, which can cause an abnormal increase in blood pressure. It is not an established fact that the wrestlers who died - supposedly from taking creatine - did so as a result of taking it. Perhaps they had to take more radical measures to make weight since the creatine caused a them to gain some and died from complications of dehydration or hyperthermia.
The bigger question is why take creatine at all? Is your training program so perfect that you can't make gains in any other way? Is your diet so perfect that you can't make gains in any other way? Do you have such a great handle on recovery and restoration that you can't make gains in any other way? Can you make modifications to any of these areas to produce a 10% net improvement instead of relying on "magic powders" to gain a 1-2% improvement in a single characteristic of fitness?