According to the Vitamin B12 Deficiency Research Group, tablets, sprays, patches or any other non-injected delivery system of B12 isn't effective for most people who are deficient. Thoughts?
https://b12researchgroup.wordpress.com/warning-about-the-use-of-b12-sublingual-tablets/
I didn't see anything against topical application on that site, only oral (including sublingual). Although I haven't seen the studies and don't know if they are actually published, the scientist who runs B12 oils and produces products for topical application says he get 80% uptake via that route. He is a reputable scientist with quite a background in B12 research so I do take him seriously.
Undoubtedly injection gives the highest uptake but topical is not far behind.
Sublingual and other oral methods are very inefficient - maybe 10% if you let the lozenges dissolve slowly.
There is less support for their claim that hydroxycobalamin is the best form for injection. It seems to be more a question of what is familiar. For reasons which are not really clear (there is no serious experimental testing of assumptions) hydrocobalamin has become accepted and widely used in the West while in Asia and especially Japan, methylcobalamin is preferred.
Way back, which cyanocobalamin was widely used, it was argued that since the upper axial ligand (cyano, methyl, hydroxy etc) gets removed when the vitamin is taken up into cells, it doesn't matter what form is used. Since cyano is easy to produce this was widely promoted.
Then people found that the hydroxy form seemed to be more beneficial in certain clinical situations. It was not clear then why this was so, nor is it clear now. There has been little investigation of mechanism but in any case, hydroxy became favoured in the West.
Similar observations in Japan led to use of methylcobalamin.
I haven't seen any direct comparison of the two in clinical trials.
There are plenty of anecdotal reports on PR of people finding a difference in the effectiveness of different forms. At this stage there is too much unknown about B12 metabolism, particularly about the effect of large doses, to be as dogmatic as that website.
You would need to try the different forms to find out which suits you.
One advantage of sublinguals is that the dose is very small. This is probably a good place to start since many people on PR report sensitivity to B12 (and folate). Rushing in to a large injectable dose might not be wise.