system
Given the following post, respond as if you're commenting on Reddit:
human
Can oral vitamin B12 work effectively if taken sublingually?
gpt
Oral absorption of B12 is variable and requires several cofactors to transport it across the intestinal mucosa. A sublingual formulation may increase absorption a little, but clinical evidence is really inconclusive on that. 
If you have a deficiency your best option is to get your levels up to the normal range via IM or SubQ injection, then you can use oral supplementation to keep those levels where they need to be.