If you are currently being treated with any of the following medications, you
should not use vitamin B1 without first talking to your healthcare provider.
Vitamin B1 should not be taken at
the same time as the antibiotic tetracycline because it interferes with the
absorption and effectiveness of this medication. Vitamin B1 either alone or in
combination with other B vitamins should be taken at different times from
tetracycline. (All vitamin B complex supplements act in this way and should
therefore be taken at different times from tetracycline.)
Antidepressant Medications, Tricylic
Taking vitamin B1
supplements may improve treatment with antidepressants such as nortriptyline,
especially in elderly patients. Other medications in this class of
antidepressants include desimpramine and imipramine.
Although the significance is not entirely clear,
laboratory studies suggest that thiamine may inhibit the anti-cancer activity of
chemotherapy agents. How this will ultimately prove relevant to people is not
known. However, it may be wise for people undergoing chemotherapy for cancer to
not take large doses of vitamin B1 supplements.
Laboratory studies suggest that digoxin (a medication
used to treat heart conditions) may reduce the ability of heart cells to absorb
and use vitamin B1; this may be particularly true when digoxin is combined with
furosemide (a loop diuretic).
Diuretics (particularly furosemide, which belongs to
a class called loop diuretics) may reduce the levels of vitamin B1 in the body.
In addition, similar to digoxin, furosemide may diminish the heart's ability to
absorb and utilize vitamin B1, especially when these two medications are
Vitamin B1 may help reduce some of the side
effects associated with scopolamine, a medication commonly used to treat motion