||As you point out, there are persistent rumors that different brands and sources of ketamine are different from other brands, sources, and forms. One of the questions that comes up is whether the Mexican brands of ketamine are somehow chemically different from the U.S. and European brands. Unfortunately we don't know where to find the information necessary to say authoritatively that they are or are not the exact same material.|
One possible explanation is that different brands of ketamine could contain different mixtures of the stereo isomers of ketamine. A difference in the relative concentrations of the different isomers could account for qualitatively different effects.
Most drugs interact with the receptors or site where they act in a specific way. The three dimensional structure of a drug can strongly dictate whether it will interact with a given receptor. Many bioactive compounds, including the building blocks of life (proteins, sugars, smaller organic molecules) can have the same functional groups attached to the same atoms but they can be arranged slightly differently or point in different directions in 3-D space. Molecules which have the same number and types of atoms and are structurally identical except for the orientation of one or more of the components are called stereoisomers. Stereoisomers that are mirror images of eachother are called enantiomers. These concepts give you D- and L- (Dextro- (right) and Levo- (Left)) sugars and R- and S- organic compounds.
A common example of a stereoisomer is ephedrine / pseudoephedrine. Pseudoephedrine is sold under the brand name Pseudaphed, while ephedrine is somewhat more stimulating and is banned for general sale in many states because of its 'non medical' uses, yet the molecules are only different in the orientation of the structural groups, which you can see using Chem Compare.
The two enantiomers of ketamine, R-ketamine and S-ketamine will have different levels of effect. It is often the case that one stereoisomer is much more active than the other, as it fits into the site of action correctly while the other is poking off the wrong way. In the case of ketamine, it has been found that the S(+) isomer is more active than the R(-) isomer. The S(+) isomer is more potent at some of the opiate and NMDA receptors and the R(-) isomer may have more effect on the heart, for instance. Drugs are often manufactured as a mixture of these isomers, as it can be very difficult to isolate one preferentially, because they are nearly identical. Thus different synthetic routes can lead to different mixtures of the final enantiomers, and will give different qualitative effects due to more or less of the more active compound in the mixture.
We do not know whether the different brands of ketamine contain, in fact, different levels of the stereoisomers of ketamine, but there are theoeretical reasons for why one pharmaceutical grade ketamine might have reliably different effects than other pharmaceutical grade ketamine. If anyone happens to know where to find information about the stereochemistry or exact constituents of different brands of ketamine, please let us know.
Another confusing element is that black market ketamine retailers and some users say that powder / chunk ketamine and liquid (solution) ketamine are somehow different chemicals from each other. Some ketamine sellers claim that the ketamine powder / rock is somehow more powerful than the ketamine which is produced pharmaceutically and sold in solution for injection. While the powder produced by one synthesis route, by a specific chemist could easily vary in quality and stereochemistry from another source, to our knowledge ketamine HCl is the only form of ketamine sold on the street in both powder and solution forms.