Yes, letrozole and vitamin B complex can be taken together safely.
There are no documented drug interactions between letrozole and vitamin B complex supplements, and concurrent use is generally safe. The FDA drug label for letrozole does not list any B vitamins as interacting substances 1. The only documented drug interactions with letrozole involve tamoxifen (which reduces letrozole levels by 38%), cimetidine, and warfarin—none of which showed clinically significant effects except tamoxifen 1.
Key Points About This Combination
No contraindications exist for taking B vitamins with letrozole based on:
- FDA labeling data showing no vitamin interactions 1
- Clinical trial data from major breast cancer studies (PALOMA-2, MONALEESA-2, MONARCH-3) that did not restrict vitamin supplementation 2, 3
- General pharmacology showing B vitamins do not affect cytochrome P450 aromatase activity
Important Considerations
While B complex is safe with letrozole, vitamin D and calcium supplementation are actually recommended for patients on aromatase inhibitors like letrozole due to increased bone loss risk 4. Research specifically shows vitamin D supplementation (2000-4000 IU daily) with calcium (1000 mg) improves musculoskeletal symptoms in letrozole-treated breast cancer patients 5.
Common Letrozole Side Effects to Monitor
The most frequent adverse effects with letrozole include 2, 1:
- Musculoskeletal pain (21-22%)
- Hot flushes (6%)
- Fatigue
- Nausea (13-15%)
- Bone density loss
B vitamins will not worsen these effects and may theoretically support general metabolic function, though no specific benefit for letrozole side effects has been proven.
Practical Recommendation
Take both medications as prescribed without timing restrictions. However, prioritize adding vitamin D (2000-4000 IU daily) and calcium (1000 mg daily) to your regimen if not already taking them, as these have proven benefits for letrozole-related bone health 4, 5.