The structure of cyclocreatine is fairly flat (planar), which aids in passive diffusion across membranes. It has been used with success in an animal study, where mice suffered from a SLC6A8 (creatine transporter at the blood brain barrier) deficiency, which is not responsive to standard creatine supplementation.  This study failed to report increases in creatine stores in the brain, but noted a reduction of mental retardation associated with increased cyclocreatine and phosphorylated cyclocreatine storages.  As demonstrated by this animal study and previous ones, cyclocreatine is bioactive after oral ingestion   and may merely be a creatine mimetic, able to phosphorylate ADP via the creatine kinase system. 
Our current understanding of adrenal function is still at its infancy at best. It is therefore very difficult for any health professional to have a good grasp of the Adrenal Fatigue condition from a purely pathological and physiological perspective. The number of physicians with true expertise in advanced Adrenal Fatigue is very small. Those who are good in this gain their expertise not from textbooks, but from years of clinical experience. There is no short cut, because text-book cases are few and far between. Because the full recovery cycle can take years to complete in severe cases, practitioners with little experience will find it hard to handle cases other than the most mild and straight forward ones.