Thiamine is a vitamin. Thiamine (vitamin B1) is important in carbohydrate (sugar and starch) metabolism, maintenance of normal growth, and transmission of nerve impulses.
Do not use thiamine if:
you are allergic to any ingredient in thiamine
Contact your doctor or health care provider right away if any of these apply to you.
Before using thiamine:
Some medical conditions may interact with thiamine. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:
if you are pregnant, planning to become pregnant, or are breast-feeding
if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
if you have allergies to medicines, foods, or other substances
if you have kidney problems
Some medicines may interact with thiamine. However, no specific interactions with thiamine are known at this time.
This may not be a complete list of all interactions that may occur. Ask your health care provider if thiamine may interact with other medicines that you take.
Check with your health care provider before you start, stop, or change the dose of any medicine.
How to use thiamine:
Use thiamine as directed by your doctor. Check the label on the medicine for exact dosing instructions.

Thiamine is usually given as an injection at your doctor's office, hospital, or clinic. If you will be using thiamine at home, a health care provider will teach you how to use it. Be sure you understand how to use thiamine.

Follow the procedures you are taught when you use a dose. Contact your health care provider if you have any questions.
Do not use thiamine if it contains particles, is cloudy or discolored, or if the vial is cracked or damaged.
Keep this product, as well as syringes and needles, out of the reach of children and away from pets. Do not reuse needles, syringes, or other materials. Ask your health care provider how to dispose of these materials after use. Follow all local rules for disposal.

If you miss a dose of thiamine, contact your doctor to find out what to do.
Ask your health care provider any questions you may have about how to use thiamine.
Important safety information:
Do not take large doses of vitamins while you use thiamine unless your doctor tells you to.
Follow the diet program given to you by your health care provider.
Tell your doctor or dentist that you take thiamine before you receive any medical or dental care, emergency care, or surgery.
Caution is advised when using thiamine in premature infants; they may be more sensitive to its effects.
Pregnancy and breast-feeding: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using thiamine while you are pregnant. It is not known if this medicine is found in breast milk. If you are or will be breast-feeding while you use thiamine, check with your doctor. Discuss any possible risks to your baby.
Possible side effects of thiamine:
All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most common side effects persist or become bothersome:
Feeling of warmth; mild tenderness or hardening at the injection site; nausea; restlessness; sweating; weakness.
Seek medical attention right away if any of these severe side effects occur:
Severe allergic reactions (rash; hives; itching; difficulty breathing or swallowing; tightness in the chest or throat; swelling of the mouth, face, lips, throat, or tongue; unusual hoarseness); black, bloody, or tarry stools; bluish skin or nails; severe or persistent stomach pain; shortness of breath; vomit that looks like coffee grounds.
Source: drugs.com