I know this this thread is very old, but in case anyone is still checking it, I thought I'd leave one more idea to check.
Long-term megadoses, even of water-soluble vitamins, can lead to unintended effects. Many vitamins have metabolic or absorption interrelationships; so if one vitamin has a high intake over a long period of time, the related ones could theoretically become deficient.
Pantothenic acid, biotin, and lipoic acid have such a relationship. For example, see http://books.google.com/books?id=iv82IDWL2JQC&pg=PA133&dq=pantothenic-acid+biotin&hl=en&sa=X&ei=DiQpUcH8DurW2wWm5IH4CA&ved=0CD4Q6AEwAg , page 133: "1) Biotin, lipoic acid and pantothenic acid share the same transport system for cellular uptake.... 2) Pantothenic acid and lipoic acid may compete with biotin for the transporter SMVT (see above); hence, supplements containing large doses of pantothenic and lipoic acid acid may decrease cellular uptake of biotin. Indeed, chronic administration of pharmacologic doses of lipoic acid decreases the activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase in rat liver to 64% to 72% of controls". I just picked a medical text at random, so if you search Google Books you should find other medical books with more information.
Anyone taking large doses of pantothenic acid or lipoic acid might inadvertently create a biotin deficiency.
Symptoms of biotin deficiency are dermatitis (scaly patches, especially around the nose and mouth), parasthesia/tingling, anemia, frequent pinkeye, irregular heartbeat, anorexia, and hair loss.
One caution: it may be tempting to simply take a biotin megadose to balance a pantothenic acid megadose, but this may not be wise, since more than just these two vitamins have interrelationships in the body. For example, blood levels of other B-vitamins, glucose, and cholesterol may be affected too. There is one study where a woman taking large doses of biotin and pantothenic acid developed a life-threatening condition ( http://www.ncbi.nlm.nih.gov/pubmed/11302404 ), and the amounts she was taking weren't outrageous (I think I read 10mg biotin and 300mg pantothenic acid) . In general, I think it's best to take the smallest effective dose of any supplement... or maybe take a megadose for only a limited time.
Hope this helps. Good luck!