Is the high dosage of b vitamins in 'gnc women's ultra mega multivitamin' cause for concern ?

No: The rda is generally not enough to promote health, only mitigate disease. High doses of b vitamins are great for stress (adrenal health), energy, memory and neuropathies. B vitamins are water soluble, so if your body doesn't need them, you will urinate them out. My concern with GNC products is that the label may not reflect what is present (vitamins and fillers/toxins).