Based on what I know, any artificial vitamins can at times do more harm than good, unless you have a defficiency. It is best to consume vitamins by eating a lot of fruits and vegetables (perferably, organic ones to avoid pesticides and other junk).

Most vitamins are sold without prescription. B-12 defficiency is quite common among elderly people, and some people that take some anti-adic medication like Prilosec. You can go to your primary medical doctor and ask him to do a blood and include a test for B-12. That way, you will know if you have a defficiency.

I read some articles that recommend B-12 supplementation even if one does not have a defficiency to maintain a healthy energy level. I checked my B-12 level and it was normal but a bit close to the lower limit. So I took some B-12. I don't think I noticed any differene, but it did not seem to hurt me (did not experience any noticeable side effects). One interesting thing about B-12 in tablets is that its absorbtion is very low, so don't be surprised to see the daily dose % on the bottle in thousands of %. Only small part of that will actually be processed by your body.

http://www.mayoclinic.com/health/vitamin-B12/NS_patient-vitaminb12