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

Some people feel more energetic within a day or two, while others notice gradual improvement over the week
If you waste money testing someones B12 levels on 3 monthly injections they are all overr the upper normal range
If you're particularly interested in B12-specific benefits, we also offer specialized options like Vitamin B12 Injectable for humans that might be exactly what you're looking for
B12 deficiency can result from dietary factors such as a lack of animal products or from conditions affecting absorption like pernicious anaemia or gastrointestinal surgery
This is why standard supplements range from 500 to 5,000 mcg