Disclaimer: None of the information in this article constitutes medical advice. All statements are merely the opinion of the writer(s). We recommend that patients follow their doctor’s guidance in regard to vitamin supplementation.

Vitamin B12 is one of the most common vitamin deficiencies in the developed world, and it's available both via oral supplementation and injection. 

But how long does it take vitamin B12 to work once you start taking it? Does it differ between method of use (oral vs. injection)? Will you feel the difference?

In this article we'll answer all of these questions and more, as we analyze clinical studies on vitamin B12 supplementation to determine how long it takes to work, and whether the method of supplementation affects its uptake.

We'll also feature reviews from real people who shared their experience supplementing with vitamin B12.

Key takeaways:

• Typically takes around one month to resolve B12 deficiency
• Oral B12 is equally effective to injectable B12
• Oral B12 may be significantly cheaper

What Does the Research Say?

There have been hundreds of clinical trials on vitamin B12 supplementation.

A clinical trial published in the American Journal of Clinical Nutrition found that in participants with vitamin B12 deficiency, oral supplementation at a daily dosage of 1,000 micrograms/day resolved deficiency in 89% of cases within one month.

A 2011 clinical trial in patients with mild B12 deficiency reported that this deficiency was resolved within one months of use, but after a subsequent three-month cessation of supplementation, deficiency re-emerged.

This suggests that oral supplementation may need to be continuous in some patient groups, with a doctor's oversight.

Intramuscular vitamin B12 injections have been shown to be equally effective to oral supplementation after around one month, according to a 2022 meta-study.

Based on the available research, we will conclude that it takes around one month of regular supplementation for vitamin B12 to work in patients with a clinical deficiency.

In patients with sub-clinical deficiencies, this timeframe may be reduced.

Do B12 Injections Work Faster?

We were surprised to discover that B12 injections do not appear to work faster than oral B12 supplementation.

One would think that because injections bypass the digestive system and get vitamin B12 directly into the bloodstream, they would be more effective than oral pills.

However, the research does not appear to bear this out, and there have been many comparative studies.

In addition to the meta-study cited in the previous section, a 2018 meta-review reported that oral B12 supplementation was equally safe and effective compared to B12 injections.

Based on the available research, we do not consider B12 injections to work faster than oral B12 supplements.

Are B12 Supplements a Better Option?

Assuming both methods of use are equally effective, oral B12 supplements may be a better overall option, because they're significantly cheaper.

According to a recent Healthline review, injectable vitamin B12 typically costs around $10 per vial out-of-pocket for American patients.

Assuming a once-weekly injection, this equates to a monthly cost of $40 for injectable B12.

Methylated B12 (the more bioavailable format) is available as an oral supplement on Amazon for $42.20 for a 6-month supply, which equates to a monthly cost of $7 for oral B12.

We consider oral vitamin B12 supplementation to be a better overall option generally, but patients should always get their doctor's approval for high-dose vitamin supplementation.

Real People Try Vitamin B12

A YouTube creator named "Dr. LeGrand" shared his experience using a B-complex oral supplement (including vitamin B12) for 30 days, in a video with over 350,000 views:

A YouTube creator named "FabFit50Plus" shared her experience trying vitamin B12 injections:

Conclusion

Vitamin B12 supplementation takes around one month to work for people with B12 deficiency, regardless of whether they're using oral supplements or injections.

Both formats of supplementation are clinically shown to resolve deficiency, and injections don't appear to work any faster than oral supplements.

This leads us to believe that oral supplements are the superior option, for both cost and convenience reasons.

Oral supplements can be less than 25% of the cost of B12 injections, even with insurance coverage.

In this article we featured real user experiences with both oral B12 supplementation and B12 injections which may be useful for readers considering which option is best for them.