its probably not true about injections causing acne.
studies also have shown sublinguals are just as effective as injections for restoring b12 deficit.
clams are also very high in b12, liver used to be prescribed way back in the day.
That about the studies showing equal effectiveness for sublingual and injecitons is true, but that about cyanocobalamin isn't, cyanocobalamin is, after all, B12, but an inactive and artificial form of it. The cyanide molecule in cyanocobalamin, albeit present in low quantities, is toxic and needs to be flushed out, and that is done by the same molecules that are needed in other more essential processes, such as reducing the homocysteine level (which is probably already high due to the B12 deficiency). 1,2
Therefore, it is not the injection per se that may cause acne-like eruptions, but instead the cyanocobalamin in it. Even if cyanocobalamin does not break you out, methylcobalamin should be preferred, as it is more effective and better absorbed.
Also, if one has a B12 deficiency, eating alone won't help much. Supplements are the only way one can take the high amount of B12 needed to solve the deficiency (also because only a low percentage of it is not excreted).
im not sure methylcobalamin can be converted into adenosylcobalamin, while as i recall cyano can be.
on the other hand hydroxycobalamin can be converted into both forms with in the body and is also a natural form found in food just like methyl and adenosyl. adenosylcobalamin is the most stored by teh body as i recall and your body can store it for a long period of time, and less so for methyl.
hydroxycobalamin is used in otehr countries to restore b12 rather then cyanocobalamin.
cyanocobalamin has longer shelf life then hydroxycobalamin.
only one company currently sells sublingual hydroxycobalamin, it is highly unstable when exposed to light and will quickly disintegrate, but has been documented in studies to be superior to cyanocobalamin injections.