Hey all first post here. I thought I will chime in with some information on creatine I have learned from reading a huge amount of literature on it.
Monohydrate- one maybe two studies say it is 100% absorbed from the intestines. Another study says it is 3% absorbed... quite a difference. Another study shows it is less than 40% absorbed same with HCL, and a few other forms of creatine. One study says about 75% of users respond to it, 25% don't. In one study it raised muscle creatine up to 40%. Can cause quite a lot of gastro intestinal distress in some people. Probably the most heavily marketed because it is the cheapest to make. I would estimate it costs around 3$ a kilo to make.
HCL- a patent says it is 50 times more water soluble than monohydrate. May be fat soluble to some extent. There is no studies on HCL alone. There is one on HCL, and 3 other forms of creatine about their intestinal absorption, and they were all less than 40% absorbed.
Ethyl ester- 15 times more absorbed from the intestines than monohydrate. Fat soluble to some degree. Crossed a cell membrane independent of the transporter in a lab experiment however in one study when given to a kid with creatine transporter deficiency- a disease where the creatine transporter on the cell membrane is broken, and so creatine can not get into the muscles, and brain, it did not increase brain creatine after 1 year on it, meaning can't get into cells without the transporter.
In my analysis HCL, and ethyl ester are probably both better than monohydrate
Free acid creatine in creactor. Also called creatine anhydrous. This is the type of creatine naturally occurring in all vertebrates including us, and is found in meat. The creatine transporter in the cell membrane is very specific to creatine- it won't take in creatinine or other structurally similar substances. It is made specifically to take in free acid creatine / creatine anhydrous so this is something to think about. It might get into muscle cells better than all the other forms of creatine. That said it does not have water attached to it like monohydrate so it may not increase muscle size to the extent monohydrate does.
All the other forms- nitrate, malate, orotate, pyruvate etc. Can only find a handful of studies on these, and there is not enough info to know for sure what they do in the body. I have not taken them myself. Someone would have to experiment with them to find out if they respond to it or not.
I have a question if someone knows- does monohydrate hit the bloodstream as monohydrate or does the water group come off, and are left with free creatine in the blood? I ask because 25% of mono people are non responders which could mean the creatine transporter does not take it up, maybe because of the water group on it.