Be sure to check the timeframes involved. Creatine is a naturally produced in your body, and you also get some from diet. Your body reaches saturation at a rate that varies by person. Some people will see near to 0 benefit from creatine as their body is already producing a near maximal amount of it. But even for those with low creatine levels, a brief loading phase (of ~25g a day for a week) and then 5g a day maintenance will generally see them at peak levels.
There's probably minimal risk of meaningful damage going overboard for a healthy person, but large doses can cause stomach issues for some people, and it seems unlikely to provide benefit beyond going beyond complete saturation. It looks like, of the studies you showed, the only one where they went for a large dosing for a long period of time was when experimenting with it on children with traumatic brain injuries. That's probably because the risk:reward skewed heavily towards reward there.
The 0 one is a meta study. It goes deeper into Huntington's 30g, Parkinson’s, elderly with cognitive decline, and supplementing for help with memory related tasks. I didn’t dive deep into all either because I saw what applied to me and decided to see the results.
I think dividing the dosages throughout the day would help offset the stomach issues some and there have been 5 year long studies showing creatine doesn’t have any major risks with 5-7% people experiencing GI issues during loading phases.
For those that don't know, if you aren't used to creatine then taking more than a few grams has a good possibility of giving you the shits (or sometimes even strong abdominal discomfort). This will (mostly) go away fairly quickly and varies drastically from person to person, but you've been warned. Best to take it on a weekend or something, and slowly build up to your max dose.
The effect is pronounced if taken with only water, all at once.
Instead you can take it throughout the day be adding it to your water bottle. Taking it with meals also typically subdues the effect.
The effect I suppose is comparable to something like magnesium citrate. I suspect they are doing similar things osmotically.
You don't need more than 3-5g per day (about 15mg per pound of body-weight) to see the maximal effects. There is a loading period where you take 2-4 weeks to saturate, many take an increased dose to get there faster but if you're going to be doing this consistently, after a month of daily usage 3-5g is all you need.
