In one study that looked at intermittent, high intensity workout, it was discovered that caffeine completely abolished the ergogenic effect (i.e., which enhances physical performance) of creatine  upplementation. Paradoxically, a
good number of the commercially available creatine supplements contain both creatine and caffeine. Another important fact is that Creatine does not seem to improve performance in exercises that requires endurance, like running, or in exercise that isn't repeated, although study results are mixed.

Short term (< 2 weeks) exercise studies have not reported any adverse events associated with creatine supplementation. Long term studies that evaluate the safety profile of long term use of creatine have not yet been run. Sporadic
reports of increased muscle cramping (especially during exercise in the heat), nausea and other gastrointestinal disturbances, elevated liver transaminases,
and acute renal injury, exist.

Dosing:

o    Loading
dose with 20 grams per day (or 0.3 grams per kg) for 5 days followed by a
maintenance dose of 2 or more grams (0.03 grams per kg) daily.

OR

o    Loading
dose of 9 grams per day for 6 days.

o    Some
sources suggest that, instead of acutely loading, similar results can be
obtained with 3 grams per day for 28 days.

During creatine supplementation, the water intake
should be increased (to avoid kidney damage) to no less than 2 liters per day.

It is worthy of
noting that creatine supplementation, in the dosages commonly used, results in
urinary concentrations that are 90 times greater than normal. This creates
potential kidney injury (nephrotoxic). So you need to keep an eye on your urine output.