Vitamin B in higher amounts can cause mania. I have experienced that concern myself as I take a full vitamin b supplement and have to avoid anything that has added vitamin b to it in larger amounts. Before I did I would experience mania. As with anything else there are noted concerns about what could be above an appropriate amount. The W.H.O. (World Health Organization) guidelines are generally the accepted figures for all vitamins and minerals and you can discuss that with your doctor.
I would doubt it is going to cause mania since your body needs it. Vitamin B deficiency can lead to a type of anemia, which can make you feel tired and low energy to begin with. It could be you're feeling some energy because you were a bit deficient before beginning to take it.
All those energy drinks, ei. 5 hr energy, are basically high doses of B vitamins with a cup of coffee worth of caffeine. I don't know that it would cause mania, but as mentioned above, in high doses could make it worse. B vitamins are like a stimulant to the brain. B deficiency causes low energy and depression, so high doses can do the opposite. I detoxed from methadone a year ago, I was taking a lot of b's and other vitamins. I had to cut them back as I healed and my need was lower. I had mental and physical side effects from too high a dose of supplements.
I have given myself Vit B shots for a yr and a half once a month. It has not caused me to be manic. I do not know if it can in some people with Bipolar but I would hope your pdoc would know for sure or perhaps research.
I just started taking vitamin B pills and it's definitely given me a much needed energy boost. I'm not sure about whether it causes mania or not in some people. But brain chemistry is so complex and individual, who knows. If it causes you to feel manic, then that's enough evidence that perhaps it's not good for you to take that much vitamin B. Perhaps you could take a lower dosage?