A blood test showed that i'm b12 deficient. serum b12 level of 186 pg/ml, should i take vitamin b12 supplements?

Absolutely: B12 in the form of methyl cobalamin is necessary for numerous biochemical pathways. It can prevent psychoses, nerve tissue degeneration and megaloblastic anemia. Methyl B12 can be given safely at doses up to 3mg intramuscularly and can be given weekly in those patients who cannot absorb it through the GI tract. Otherwise, 2mg oraly is optimal. There are no known side-effects of having to much.

B12: this low will likely cause dementia, spinal cord degeneration and peripheral neuropathy. Keep your level above 550 for the rest of your life. Recovery takes about a year in a young person. I suggest you take liquid sublingual weekly for 3 months then bi weekly thereafter. Its important to check a level after you cut back to twice a month. Use 1 1/2 dropper and hold it under the tongue for 30 sec.