Oh heck no. I'm on nearly 400 mg of Metoprolol Succinate in divided doses, and 500 mg of Dilantin in divided doses, and taking Ranitidine (Zantac), Singulair, and Xyzal (all three of those for Chronic Urticaria) and Zocor for Cholesterol, according to literature, I should be a babbling sleepwalker, but honestly, I feel fine.

Results vary between individuals, in no way, shape, or form am I insinuating that certain people aren't experiencing brain fog even with lower doses, we all react differently to medications, I just wanted to assure you Brain Fog isn't necessarily a result.

One caveat. Dilantin can depress Vitamin D levels, and lack of sunlight in the winter the same, and at one time I'd get Seasonal Affective Disorder (SAD) so on my own, I started taking 2000 IU of Vitamin D3 once a day, 365 days of the year, and it made a HUGE difference in my Seasonal Depression, I'm not sure if it helps with cognition too. Always consult with your doctor or pharmacist before adding supplements, either vitamin or minerals.

Here's just one of the interactions possible between Vitamin D3 and one of the prescriptions I take, but my doctors are aware that I take it and the Neurologist tested me to be sure I was taking enough, which I am. Plus I'm not taking a High Dose of vitamin D3:

""MONITOR: Coadministration of thiazide diuretics with high dosages of calcium and/or vitamin D has been associated with reports of hypercalcemia in some patients. Thiazide diuretics inhibit the renal excretion of calcium and may also enhance responsiveness of bone and renal tubule to parathyroid hormone, thus concurrent use of large amounts of calcium or vitamin D can lead to excessively high plasma levels of calcium. Patients who are particularly susceptible include those with hyperparathyroidism, those being treated for osteoporosis, and those receiving high dosages of vitamin D for hypoparathyroidism. Metabolic alkalosis and the milk-alkali syndrome have been reported during prolonged therapy with thiazide diuretics and calcium.""