In clinical trials at the 12 mg dose, researchers documented nausea in 28% of participants, diarrhea in 23%, constipation in 17%, and vomiting in 12%
This includes: Patients with malabsorption issues due to gastrointestinal disorders Individuals with pernicious anemia or other conditions that impair B12 absorption Cases where a rapid increase in B12 levels is necessary In these cases, IV delivery gets B12 straight into the blood
Suitability before injection Tell the team about previous B12 treatment, allergies, medicines, pregnancy status where relevant, and any diagnosis or blood results you already have
Seek immediate medical attention (call 999 or go to A&E) if you experience: Signs of a severe allergic reaction such as swelling of the face, lips, tongue or throat, difficulty breathing, or severe widespread rash Blood in stools or vomit , which may indicate gastrointestinal bleeding requiring urgent assessment Contact your GP urgently if you experience: Severe or persistent abdominal pain that does not resolve within a few days or worsens over time Persistent vomiting that prevents you from keeping down food, fluids, or medications Severe diarrhoea lasting more than 48 hours, particularly if accompanied by dehydration signs (reduced urination, dizziness, dry mouth) New or worsening symptoms after starting B12 supplementation that significantly impact daily activities or quality of life Routine review is appropriate when: Mild symptoms persist beyond three weeks despite adjusting timing, dose, or formulation You are uncertain whether symptoms relate to B12 supplementation or another condition You have pre-existing gastrointestinal conditions (such as Crohn's disease, coeliac disease, or gastritis) and experience new digestive symptoms You require guidance on alternative supplementation routes, particularly if oral preparations consistently cause discomfort It is important to remember that many gastrointestinal symptoms have multiple potential causes
Typical cycles run four to eight weeks, sometimes longer for chronic tendon issues
Hydroxocobalamin and adenosylcobalamin also exist but see less use in standard wellness care settings
