You can often feel the effects of a B12 injection within 24 to 72 hours, with increased energy, clearer thinking, and better mood being common first signs, though it depends on your deficiency's severity, with severe cases taking longer. Immediate benefits occur because the shot bypasses digestion, working directly in the bloodstream, but full recovery of depleted stores can take weeks.
Hydroxocobalamin starts to work straight away. However, it may take a few days or weeks before your vitamin B12 levels and symptoms (such as extreme tiredness or lack of energy) start to improve. Are there any long-term side effects? It's OK to have hydroxocobalamin injections for a long time.
Feeling energized after your B12 shot is a great sign! However, don't let that newfound energy lead you straight into a super-intense workout session. It's best to take it easy for the next 24 hours, especially if you're not used to strenuous activity.
Typically, our patients experience positive effects between 24-72 hours after the treatment. People with severe deficiencies may require a few injections to start feeling the benefits and will be overseen by a medical professional to ensure accurate dosage to optimise results.
Some researchers have studied vitamin B-12 to find out if it can raise energy and endurance during exercise. But there isn't evidence to prove this. And unless you have low vitamin B-12 levels in your body, vitamin B-12 shots aren't likely to give you more energy or improve your performance.
Individuals experiencing a deficiency often report feeling unusually tired or weak, even after adequate sleep. This symptom arises because a lack of B12 impairs the production of red blood cells, leading to fewer cells to transport oxygen throughout the body.
To ensure your treatment is working, you may need to have further blood tests. A blood test is often carried out around 7 to 10 days after starting treatment to assess whether treatment is working. This is to check your haemoglobin level and the number of the immature red blood cells (reticulocytes) in your blood.
Your doctor likely stopped B12 injections due to following standard guidelines suggesting oral supplements or for reasons like cost/logistics (especially during the pandemic), but this can be risky; the main reasons are often a perceived 'normal' blood test (which doesn't always reflect cell levels) or a guideline shift, but you may still need injections for neurological symptoms or poor absorption, so discuss your symptoms urgently with your doctor and ask for clear evidence for the change.
Helps Improve Sleep Patterns
Vitamin B12 is a major factor in the tryptophan production process. B12 injections can help you go from restless nights to getting a good night sleep.
Common side effects
Hydroxocobalamin and pregnancy
Hydroxocobalamin can be used during pregnancy. It's important that a vitamin B12 deficiency is correctly treated to make sure that you and your baby are healthy.
To ensure your treatment is working, you may need to have further blood tests. A blood test is often carried out around 7 to 10 days after starting treatment to assess whether treatment is working. This is to check your haemoglobin level and the number of the immature red blood cells (reticulocytes) in your blood.
Cutaneous acneiform eruptions are a side effect of many medications, including vitamin B12 therapy. However, reports of vitamin B12–induced acne are rare.
Symptoms of high B12 levels
High B12 levels can cause the following symptoms: Acne or redness affecting your face. Anxiety. Chromaturia, which makes your pee look red but isn't the same as hematuria.
Estrogen, which is typically higher in females, may suppress testosterone synthesis (24), and vitamin B12 might amplify this effect by enhancing estrogen activity or synthesis (25). Additionally, vitamin B12's role in reducing homocysteine levels could influence metabolic pathways linked to hormone regulation (26).
While Vitamin B12 is generally safe, potential disadvantages (side effects) can occur, especially with high doses or injections, including headaches, nausea, diarrhea, weakness, skin issues (rash, itching), and rarely, more serious heart or allergic reactions (like anaphylaxis), though toxicity from oral intake is rare as excess is usually excreted. Conversely, a deficiency can cause serious problems like irreversible nerve damage, memory loss, fatigue, infertility, and increased risk of certain cancers, making proper intake crucial.
B12 deficiency can trigger specific food cravings, most notably for meat, fish, or eggs, as the body seeks animal-based sources to replenish the vitamin, especially in those on vegetarian/vegan diets or older adults. While cravings for sugary or salty foods can also signal general B-vitamin issues, the distinct urge for protein-rich animal products is a key indicator, but professional testing is crucial for confirmation.
Symptoms of vitamin B12 or folate deficiency
Wondering how you'll feel after B12 shots? Our patients often report the following: Immediate boost in energy and relief from fatigue within the first few hours or days. Long-term impact for those with documented B12 deficiency over the course of regular monthly injections.
In fact, some studies have even suggested the opposite. For instance, one study noted that individuals who regularly took vitamin B12 supplements gained between 2.5 to 17 fewer pounds (1.2 to 7.7 kg) over a decade than those who didn't supplement.
Vitamin B12 is involved in the breakdown of a protein called homocysteine. High homocysteine levels are associated with an increased risk of heart disease and stroke as it may promote the formation of blood clots and excess free radical cells, and may impair normal blood vessel function.
Disturbed or blurred vision can also occur as a result of a Vitamin B12 deficiency. This happens when the deficiency causes damage to the optic nerve that leads to your eyes. The nervous signal that travels from the eye to the brain is disturbed due to this damage, leading to impaired vision.
Symptoms such as pins and needles, disturbed vision, a sore and red tongue, mouth ulcers, muscle weakness and problems with balancing and walking, psychological problems such as depression and confusion, problems with memory, understanding and judgement could also be related to B12 deficiency.