Depends on your training and what kind of results you're after. Anything over 10g a day for long periods of time doesn't do much as there's a distinct upper limit to creatine stores. Most people do well on just 5g a day. I don't recommend loading since I don't feel it's necessary but I'm sure others will tell you it's better. If you're just looking for a temporary strength boost (as in the final week of a training cycle) you can use 15-20g a day for a week or so. The only real side-effects of large, short-term doses of creatine is possible intestinal discomfort.
Originally posted by growinUP ..........and also headaches can be a problem.
I have never heard that. I assume you mean that creatine pulls so much water into your muscle cells that there's not enough left over for the brain? (Seems unlikely if you're properly hydrated.) Cause otherwise I don't see how creatine could have that effect.
Some other members who agree with me:
-LeeJB
-9inarow
-Sophos9
Do a thread search "creatine" and "headaches" and see what you come up with.
I would like to add that I usually drink 3-4 litres of water per day plus an additional 1-2 litres during a workout. When I get creatine induced headaches I drink as much water as I can and still to no avail. They kick in as soon as I exceed 5-7 grams of creatine in a day.