Vitamin B complex refers to the following vitamins: thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folic acid and cobalamin. Each type of B vitamin interacts differently with certain types of medications. However, all B vitamins interact similarly with tetracycline, an antibiotic. B vitamins prevent the absorption of tetracycline and interferes with its activity. You should never take B vitamins concurrently with tetracycline. Consult with your health care provider before taking any vitamin supplements if you are also taking other medications.
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Thiamin or Vitamin B1
Case reports have shown that taking thiamin concurrently with 5-Fluorouracil – a cancer-therapy drug -- or diuretics can induce thiamin deficiency. Taking phenytoin, a medication for seizures, for a prolonged duration also reduces thiamin level in the blood.
A lack of thiamin over many calendar days can impair various tissues -- from the heart to the brain. Your body needs thiamin for a healthy nervous system, energy metabolism and normal appetite (see references 1).
Riboflavin or Vitamin B2
Certain anti-psychotic, anti-malarial and cancer chemotherapy medications can prevent riboflavin from converting into FAD and FMN – molecules involved in energy metabolism. Your risk of becoming riboflavin-deficient increases proportionately with your intake of the anti-seizure medication phenobarbital over a number of days. Excess phenobarbital will stimulate your liver to release enzymes – specialized proteins – to destroy riboflavin.
Riboflavin deficiency interrupts energy metabolism, and leads to skin and vision health problems, such as hypersensitivity to light, red eyes, cracks on the lips, skin rash and purplish-red, swollen and sometimes pain in the tongue.
Niacin or Vitamin B3
In a few cases, the concurrent intake of niacin and lovastatin -- cholesterol-reducing medications -- has induced rhabdomyolysis, a condition of fragmented muscle fibers and the release of its contents in the blood. Rhabdomyolysis augments the risk of kidney failure.
Pantothenic acid or Vitamin B5
Pantothenic acid may boost the activity of Alzheimer’s disease medications, and can produce serious side effects. Do not take vitamin B5 if you are also on medication for Alzheimer’s, unless you have your physician's approval.
Pyridoxine or Vitamin B6
The following medications can decrease the levels of vitamin B6 in the blood, and increase your risk for vitamin B6 deficiency: cycloserine and isoniazid, for tuberculosis; hydralazine, for high blood pressure; penicillamine, for rheumatoid arthritis; theophylline, for asthma; monoamine oxidase inhibitors, for depression; and erythropoietin, for anemia.
Vitamin B6 can diminish the activity of these following medications: levodopa, for Parkinson’s disease, and phenytoin, for seizures (see references 5).
Vitamin B6 deficiency can induce anemia, abnormal brain activity, mood disorders, muscle twitching and seizures (see references 5). Vitamin B6 deficiency also weakens your immune system.
Biotin or Vitamin B7
Anticonvulsant drugs, used to treat seizures, can interfere with the absorption of biotin. Furthermore, an intake of sulfa drugs over a long period of time can decrease the production of biotin from bacteria, found naturally in your intestines.
A deficiency in biotin can cause hair loss, poor appetite, nausea, depression, muscle pain, weakness, fatigue, dry skin, rash and abnormal heart activity.
Folic acid or Vitamin B9
The following medications decrease folic acid absorption and its activity: metformin, for type 2 diabetes and abnormal blood sugar level; sulfasalazine, for Crohn’s disease and ulcerative colitis; triamterene, a diuretic; methotrexate, for cancer and rheumatoid arthritis; barbiturates, for sedatives; and anticonvulsants.
Folic acid deficiency can lead to anemia, heartburn, diarrhea, constipation, frequent infections, depression, mental confusion and fainting.
Cobalamin Vitamin B12
Chloramphenicol, an antibiotic, may inhibit the response of red blood cells to vitamin B12 and metformin, prescribed for diabetes, may decrease the absorption of vitamin B12.
Vitamin B12 deficiency produces anemia, fatigue and hypersensitivity, and degenerates your nervous system, leading to paralysis.