What the label lists and what reports show
Cyanocobalamin side effects
Cyanocobalamin's FDA label lists its adverse reactions in its own words. FAERS holds 32,744 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is fatigue (3,333 reports).
- Generic listed
Check it at the source: the cyanocobalamin FDA label on DailyMed (effective October 31, 2023, American Regent, Inc.); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of Cyanocobalamin Nasal Spray?Cyanocobalamin Nasal Spray can cause serious side effects, including: • Weaken your eye nerve in patients with early Leber’s disease. Tell your healthcare provider if you or your family has a history of early Leber’s disease. • Serious allergic reactions. Serious life-threatening allergic reactions including death have happened in people who have received vitamin B 12 by injection or by intravenous (IV) infusion (parenteral). Tell your healthcare provider if you have ever had a reaction after you received vitamin B 12 by injection or IV infusion. • Hiding (masking) a folate deficiency. Your healthcare provider may do certain blood tests to check your vitamin B 12 and folate levels. • Low potassium levels (hypokalemia) and low blood platelets (thrombocytopenia) can happen in people with serious megaloblastic anemia. […]
Source: FDA drug label (cyanocobalamin), Padagis Israel Pharmaceuticals Ltd, effective February 28, 2023 (SPL set 971e5f30-55c2-4193-9dd8-b43a1862b92a), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsGeneralized: Anaphylactic shock and death have been reported with administration of parenteral vitamin B 12 (see WARNINGS ). Cardiovascular: Pulmonary edema and congestive heart failure early in treatment; peripheral vascular thrombosis. Hematological: Polycythemia vera Gastrointestinal: Mild transient diarrhea Dermatological: Itching; transitory exanthema Miscellaneous: Feeling of swelling of entire body
Table 1. Adverse Reactions Following Intranasal or Intramuscular Administration of Cyanocobalamin In Vitamin B12 Deficient Patients in Hematologic Remission
This table is printed in the Cyanocobalamin label published by Lupin Pharmaceuticals,Inc. of August 24, 2023; the label quoted above does not print one.
| Reaction | Adverse Reaction Another Cyanocobalamin Nasal Formulation, 500 mcg (n=24) | Number of Patients (%) Intramuscular Cyanocobalamin*, 100 mcg (n=25) |
|---|---|---|
| Infectiona | 3 (13) | 3 (12) |
| Headache | 1 (4) | 5 (20) |
| Asthenia | 1 (4) | 4 (16) |
| Nausea | 1 (4) | 1 (4) |
| Glossitis | 1 (4) | 0 (0) |
| Paresthesia | 1 (4) | 1 (4) |
| Rhinitis | 1 (4) | 2 (8) |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
Source: FDA drug label, American Regent, Inc., effective October 31, 2023 (SPL set 2fb653d6-e2b2-4969-831b-c0dc37b9c0cc), via openFDA; the full label on DailyMed
What do FAERS reports show?
32,744 reports list cyanocobalamin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 3,282 are coded as a death and 13,233 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 21 reactions below, 4 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Cyanocobalamin: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions