Drug interaction with vitamin B12

Vitamin B12
Forms: Cobalamin, cyanocobalamin, and hydroxy cyanocobalamin
Sources: Liver, meat, saltwater fish, oysters, milk, eggs, and generally all foods of animal origin.
* Interactions:
Cholestyramine:
Mechanism: Absorbent and degrading compounds of bile acids such as cholestyramine reduce the digestion and absorption of fats, fat-soluble vitamins, and other micronutrients such as vitamin B12.
Recommendation: In people who take cholestyramine, it is recommended to use a multivitamin-mineral with a few hour's distances from cholestyramine.

Cimetidine:
Mechanism: Cimetidine inhibits the secretion of gastric acid and pepsin by preventing the separation of vitamin B12 in the diet from the protein complex attached to it and reducing the absorption of vitamin B12, resulting in poverty in people who take cimetidine for a long time. 
Recommendation: Vitamin B12 in supplements is not needed for absorption of stomach acid, so it does not interfere with cimetidine and other similar drugs. For people who take cimetidine for a long time, it is recommended to take 10 micrograms of vitamin B12 daily, which is present in most multivitamins and B-complexes in these amounts.
Amount and method of taking vitamin B12
Read the package leaflet carefully before starting treatment with this medicine. This brochure will help you to get comprehensive information about the drug and its possible side effects.
The dose and amount of vitamin B12 vary from person to person; Use the medicine exactly as your doctor advised. Different types of vitamin B12 (pills, chewable tablets, syrups) are sold in pharmacies, the amount and type of use of each are different, prepare a type of this vitamin that your doctor has prescribed for you.
If you forget to take your daily dose at the right time, do not worry, do not take the missed dose. You should not take two doses of the medicine together because of the missed dose.

Contraindications to vitamin B12
Pay attention to the expiration date of vitamin B12 and do not take it if your medicine has expired.
Never give vitamin B12 to another person, even if you have the same symptoms.
Check for vitamin B12 drug interactions, and if you are taking a drug that interacts with this medication, talk to your doctor about using your medications.
Vitamin B12 intake during pregnancy and lactation
During pregnancy and lactation, you should not use the drug arbitrarily without consulting your doctor. Medications can have devastating effects on the fetus or yourself. Your doctor may prescribe this vitamin for you during pregnancy, use this vitamin if your doctor prescribes it.

Special warnings and precautions while taking vitamin B12
Some medications cannot be prescribed under certain conditions, and some medications may be prescribed if additional treatment is needed; Therefore, it is best to let your doctor know the following before taking this medicine:
If you are pregnant or breast-feeding.
If you have any of the following conditions, talk to your doctor or pharmacist before using this medicine: Specific eye disease (optic nerve neuropathy), gout, iron deficiency or low folic acid deficiency, low potassium levels.
If you are taking certain medications. These medicines include all the medicines available, whether they  are prescribed for you or not, such as herbal medicines and supplements.