Hi Curry, The 5mg Jarrow sublingual when held for that 45-120 minutes under the upper lip results in the absorption of 750-1250mcg, fully equivalent to a 1mg injection of mb12 at a far lower cost and with a much greater reliability. The Jarrow and Enzymatic Therapy sublingual b12s have neurological qualities that I have never seen exceeded by any injectable and at best equaled by some. If you have performed the titration I have defined elsewhere and then when equilibrium has been reached tried a 50mg single dose sublingual mb12, and it has an effect on the central nervous system, then, because of quantity needed I would say that injections of at least 7.5mg at least once a day is justified. Otherwise my opinion is that injecting is not worth the trouble. I inject 30mg daily as 3 doses of 10mg and that is the amount by titration I need to maintain and even improve neurological functioning in my already damaged nervous system. Most people top out on healing at perhaps 2-4mg in serum per day, as does my body. More then makes do difference until one hits the threshold for CNS diffusion IF they have trouble getting cobalamin into the CSF, and this applies separately to adenosylb12 and methylb12. I need both in the CNS and have worked out how to do the adenosylb12 sublinguially and ride into the CNS/CSF with a mb12 injection. That way I take 18mg of adb12 once a week starting 1-2 hours after an mb12 injection. If you have not done the titration and if you get a good batch of injectable mb12 and you just start with an injection of almost any size you may find the onset to be overwhelming. Many folks take several months to complete the titration up to a level where they can test if an injection would help and where they would not be overwhelmed with it. The injectable mb12 is generally a prescription item. It is made up by compounding pharmacies and the quality is widely variable for some controllable reasons and some that can't be controlled.