Can Methycobal Cause Fever? A Closer Look at Methylcobalamin Side Effects

October 8, 2025 •

3 min read

While Methycobal (methylcobalamin) is generally well-tolerated, reports show that a small percentage of patients receiving injectable forms of vitamin B12 may experience a fever. Though uncommon, it is important for users to understand the potential reasons behind this and to know when to seek medical advice for fever or other side effects when taking Methycobal.

Quick Summary

A fever is not a common side effect of Methycobal, a vitamin B12 medication. It could signal a rare allergic reaction or an injection site response, though mild side effects like headache or nausea are more likely. In some cases, fever is a symptom of the underlying B12 deficiency being treated.

Key Points

Fever is a Rare Side Effect: Fever is not a common or typical adverse effect of Methycobal (methylcobalamin).
Allergic Reactions Can Cause Fever: A severe allergic reaction, though rare, can present with a fever, rash, swelling, and difficulty breathing, necessitating immediate medical attention.
Injections May Cause Local Reactions: For injectable forms, localized pain, redness, or swelling at the injection site is possible, which may feel warm, but this is distinct from a systemic fever.
B12 Deficiency Can Cause Fever: In some cases, the fever may be a symptom of the underlying megaloblastic anemia or B12 deficiency being treated, and it will resolve with treatment.
Consult a Doctor for Any Fever: A healthcare provider should be consulted for any fever that develops after taking Methycobal to determine the cause and rule out a serious reaction.
Other Side Effects are More Common: Less serious side effects like nausea, headache, dizziness, and injection site pain are more frequently reported than fever.
Methycobal is an Active Form of B12: Methycobal (methylcobalamin) is a natural and active form of vitamin B12, unlike the synthetic cyanocobalamin.

What is Methycobal (Methylcobalamin)?

Methycobal is a brand name for methylcobalamin, a form of vitamin B12. Vitamin B12 is essential for numerous bodily functions, including nerve tissue health, brain function, and red blood cell formation. Methycobal is commonly prescribed to treat conditions like vitamin B12 deficiency, peripheral neuropathy (nerve pain in the hands and feet), and megaloblastic anemia. It is available in both tablet and injectable forms.

The Link Between Methycobal and Fever

While Methycobal is generally considered safe, some users may experience side effects. A fever is not a typical side effect but can occur in certain circumstances, and it is crucial to understand the context. Possible connections between Methycobal and fever include:

Rare Allergic Reactions: One of the most serious, though uncommon, scenarios is a severe allergic reaction to the medication. This can manifest with symptoms that may include a fever, along with a rash, itching, hives, and swelling. These are serious signs requiring immediate medical attention.
Underlying B12 Deficiency: In cases of severe B12 deficiency causing megaloblastic anemia, a low-grade fever is sometimes a symptom of the disease itself. As the condition is treated with Methycobal, the fever should resolve. In such instances, the fever is related to the illness, not the treatment.
Injection-Related Reactions: For individuals receiving Methycobal injections, less serious side effects like pain, redness, or swelling at the injection site are possible. Some reports have also noted a "feeling hot" sensation or flushing, though a high fever is less common. This is often a localized response, not a systemic fever.

Distinguishing Between Minor and Serious Reactions

It is important to differentiate between a localized, mild reaction and a systemic, severe one. If you experience a fever after taking Methycobal, consider the presence of other symptoms to help determine the severity.

Serious Signs (Seek Immediate Medical Attention):

Rash, hives, or severe itching
Swelling of the face, lips, tongue, or throat
Difficulty breathing or wheezing
Chest tightness
Unusual hoarseness
Passing out or severe dizziness

Common, Less Serious Signs (Consult Doctor if Persistent):

Injection site pain or redness
Mild headache
Nausea or vomiting
Diarrhea
Dizziness
Loss of appetite

Understanding Different Forms of B12

Methycobal contains methylcobalamin, which is the active form of vitamin B12. It differs from cyanocobalamin, another common form of B12.


Feature	Methylcobalamin (Methycobal)	Cyanocobalamin
Sourcing	Natural form of Vitamin B12	Synthetic form of Vitamin B12
Bioavailability	Readily usable by the body, directly active	Must be converted by the body into an active form
Retention	Better retained in the body over time	Higher urinary excretion, potentially lower retention
Safety	Considered safe when used as directed	Contains trace, minimal levels of cyanide, considered safe
Cost	Generally higher cost	Less expensive and widely available

When to Seek Medical Advice

If you develop a fever or any other concerning symptoms after taking Methycobal, you should contact your doctor. While a fever is not a typical side effect, it can sometimes indicate an allergic reaction that requires prompt medical evaluation. It is also important to rule out that the fever is not a symptom of your underlying medical condition or another unrelated illness. A healthcare professional can help you determine the cause of your symptoms and recommend the appropriate course of action.

Conclusion

In summary, while it is possible for a fever to occur in some individuals taking Methycobal, it is not a common side effect. The presence of a fever should be investigated by a doctor to distinguish between a rare allergic reaction, a localized injection site issue, or a symptom of the underlying medical condition being treated. Always inform your healthcare provider of any unusual symptoms or side effects, especially if they are severe or persistent. Most individuals tolerate Methycobal well, experiencing minimal or no side effects at all.

For more detailed information on side effects, refer to resources like Drugs.com, which provides a comprehensive list of known adverse reactions associated with methylcobalamin.

Frequently Asked Questions

It is not a common side effect to get a fever after a Methycobal injection, though some people report feeling warm or having localized redness and swelling at the injection site. A fever could signal a less common systemic reaction or an underlying condition, so you should contact your doctor to be safe.

An allergic reaction fever is typically accompanied by other symptoms like a rash, hives, swelling of the face or throat, and difficulty breathing, which require immediate medical help. A fever from a separate illness would have its own set of symptoms, while a fever related to the underlying B12 deficiency would likely resolve with treatment.

Yes, it is possible. Severe vitamin B12 deficiency, especially when it leads to megaloblastic anemia, can cause a low-grade fever. This fever typically subsides once treatment with B12, such as Methycobal, begins.

If you develop a fever, you should contact your healthcare provider. They can help determine if it is a side effect of the medication, a sign of an allergic reaction, or caused by another unrelated issue. Always seek immediate medical help for severe symptoms like swelling or breathing difficulty.

More commonly reported side effects of Methycobal include nausea, vomiting, headache, diarrhea, and dizziness. For injections, localized pain, redness, and swelling at the injection site are also common.

While not a primary side effect, some comprehensive lists of potential vitamin B12 injection reactions do include chills, night sweats, or hot flushes. If you experience these, especially in conjunction with other symptoms, it is best to consult your doctor.

You should not continue taking Methycobal without first consulting your doctor if you have a fever. They will need to evaluate the situation to ensure the fever is not a sign of a more serious allergic reaction. Stopping or continuing the medication should be done under medical supervision.