Guar Gum - Femara (Letrozole) Interaction
Herbal: Guar Gum
Also Known As: Dietary Fiber, Farine de Guar, Fibre Alimentaire, Goma Guar, Gomme de Guar, Gomme de Jaguar, Guar Flour, Indian Cluster Bean, Indian Guar Plant, Jaguar Gum, Partially Hydrolyzed Guar Gum, PHGG, Cyamopsis tetragonoloba
Drug: Letrozole
Brand names:
Femara
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
May 18, 2025
Interaction Details
Letrozole is classified as belonging to the following category: Oral Drugs
Guar gum might reduce the absorption of some oral drugs, potentially decreasing their effectiveness.
Clinical research shows that guar gum reduces or slows absorption of medications such as penicillin and metformin. To avoid changes in absorption, take guar gum 30-60 minutes after oral medications.
Interaction Rating
Likelihood of Occurrence
PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
References
- Gin H, Orgerie MB, Aubertin J. The influence of Guar gum on absorption of metformin from the gut in healthy volunteers. Horm Metab Res 1989;21:81-3.
- Huupponen R, Seppala P, Iisalo E. Effect of guar gum, a fibre preparation, on digoxin and penicillin absorption in man. Eur J Clin Pharmacol 1984;26:279-81.
Guar Gum Overview
Guar gum is a type of fiber that is derived from the seeds of the guar plant, which is native to India and Pakistan. It is a water-soluble, gel-forming fiber that is often used as a thickening agent or stabilizer in a variety of products. In addition to its use as a thickener, guar gum has also been studied for its potential health benefits, including its ability to lower blood sugar levels and improve bowel function, much like traditional fiber products.
Letrozole Overview
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Letrozole is used treat early breast cancer in women who have experienced menopause (change of life; end of monthly menstrual periods) and who have had other treatments, such as radiation or surgery to remove the tumor. It is also used to treat early breast cancer in women who have experienced menopause and who have already been treated with a medication called tamoxifen (Nolvadex) for 5 years. Letrozole is also used in women who have experienced menopause as a first treatment of breast cancer that has spread within the breast or to other areas of the body or in women whose breast cancer has worsened while they were taking tamoxifen. Letrozole is in a class of medications called nonsteroidal aromatase inhibitors. It works by decreasing the amount of estrogen produced by the body. This can slow or stop the growth of some types of breast cancer cells that need estrogen to grow.
Guar Gum - More Interactions
Guar Gum interacts with 1990 drugs
Interaction Rating Key
These severity listings are for informational use only. Never start, stop or otherwise change your therapy before speaking with your provider.
| Major | The combined use of these agents is strongly discouraged as serious side effects or other negative outcomes could occur. |
| Moderate | Use cautiously under the care of a healthcare professional or avoid this combination. A significant interaction or negative outcome could occur. |
| Minor | Be aware that there is a chance of an interaction. Watch for warning signs of a potential interaction. |
| Unknown | No interactions have been reported or no interaction data is currently available. |
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Parts of this content are provided by the Therapeutic Research Center, LLC.
DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.
© 2021 Therapeutic Research Center, LLC
Drug descriptions are provided by MedlinePlus.
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In addition to being a clinical pharmacist specializing in pharmacotherapy, Dr. Brian Staiger is a registered herbalist through the American Herbalist Guild. He has combined his passion for pharmacy practice with the study of medical ethnobotany to improve patient care. Feel free to reach out about any of your herbal or medication questions!
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