• Alyssa Fontaine, RD
• Mar 09, 2026

How Long Do B12 Supplements Take to Work?

Vitamine B12 supplements are typically used to treat deficiency, helping support things like nerve function, red blood cell production, and creating energy your body can use from the food you eat.

One of the most common questions we receive from our own clients as vegan dietitians and nutritionists are things like:

Will I have to take B12 supplements forever? When can I stop?

How long will it take before I feel better?

But don’t worry, in this article we will break down how B12 supplements work, and answer these key questions about vitamin B12.

How B12 Supplements Work in the Body

When your body runs low on vitamin B12, a supplement can act to help refill and return those stores to normal. B12 is vital for your body, and as vegan dietitians, we will list some of the many reasons you need it.

Key functions of B12:

• Has a crucial role in new red-blood cell formation
• Helps prevent megaloblastic anemia
• Keeps your neurological and nervous system healthy
• Is a key component in converting the food you eat into energy your body can use

How Long Does It Take to Feel the Effects?

If you recently started taking B12, it’s only natural to wonder how long it actually takes to replenish your stores. Improvements can start as soon as a few days to a few weeks of starting supplements; however, it’s not that simple. Your full recovery will depend on the symptoms and severity of the deficiency itself.

Here is what you can expect:

• Improvements in your energy levels and fatigue: days to weeks
• Better red blood cell production: 1-2 months
• Neurological symptom improvements: several months
  • Note that in severe cases, neurological symptoms may not fully resolve.

Factors That Affect How Quickly B12 Works

Before you start taking B12 supplements, there are a few things about absorption you should keep in mind;

1. Severity of your deficiency matters: As we mentioned previously, the worse the deficiency, the longer it will take to correct it
2. Type of supplement: There are different forms of B12 supplements, however, the fastest acting method is injections, which may be warranted in certain conditions.
3. Your body’s ability to absorb B12: Everyone is unique, and that applies to the way we absorb things. That said, certain conditions like pernicious anemia or digestive disorders can affect B12 absorption.
4. Dose and consistency: Building a routine and consistently taking your supplements is key to be able to restore and maintain B12 levels.
5. Underlying cause of the deficiency: The reason will affect the pace of the recovery itself. When a deficiency comes from low B12 in your overall diet, it will likely respond faster than deficiencies that are caused by medical conditions.

Signs Your B12 Supplement Is Working

As plant-based nutritionist and dietitians, here are some tell-tale signs that your B12 are improving and your deficiency may be starting to resolve:

Common signs

• Better energy and less fatigue
• Improved concentration and mental clarity
• Improved anemia related symptoms (fatigue, weakness, pale/yellowish skin, dizziness, etc.)
• Less numbness or tingling in certain cases

How Long Should You Take B12 Supplements?

Given everything we have shared so far, you may have guessed the answer to this one. It depends.

Because a deficiency can vary based on what caused it, some of our clients have needed B12 for a short period of time, while others (especially when following a vegan diet or with digestive disorders) could require long-term supplementation.

Connecting with healthcare providers, such as a vegan dietitian and your family doctor, is essential to determine the outlook of your supplementation.

The Bottom Line: How Long Do B12 Supplements Take to Work?

Vitamin deficiencies can be frustrating, we get it. As vegan dietitians, B12 can be especially tricky since it is primarily found in animal sources, making it harder to get it nutritionally (Check out this article made by some of our dietitians for ideas on vegan sources of B12).

Remember that staying aware and in-tune with your body means you can catch these kinds of deficiencies early, and potentially recover quicker than catching them later down the line.

Most importantly, keep in mind that a deficiency is not necessarily your fault, especially because it depends on absorption, individual conditions, which are not in our control. What is in our control is our nutrition, and that’s what we are here to help with. Connect with one of our vegan dietitians to learn how to best optimize your diet to minimize your risk of a vitamin B12 deficiency.