Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have a serious side effect such as:
blue colored lips;
chest pain, feeling short of breath;
black, bloody, or tarry stools; or
coughing up blood or vomit that looks like coffee grounds.
Less serious side effects may include:
nausea, tight feeling in your throat;
sweating, feeling warm;
mild rash or itching;
feeling restless; or
tenderness or a hard lump where a thiamine injection was given.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Thiamine side effects (more detail)
