From this thread.
http://www.longhaircareforum.com/showthread.php?t=105394
B-Complex vitamin; 50mg taken once or twice a day- B-complex vitamins are actually a group 8 vitamins. Thiamine(B1), Riboflavin(B2), Niacin(B3),
Pyridoxine(B6), Folic Acid(B9), Cyanocobalamin(B12), Pantothenic Acid(B5), and Biotin. Biotin is sometimes referred to as Vitamin H.
As a whole, B-complex vitamins are involved breaking down protien, carbohydrates, and fats. B-vitamins help make DNA, bloodcells, maintain nerves and your gastrointestinal tract. When it comes to your hair, they help extend the growth cycle so that you can enjoy a longer period of hair growth.
Biotin is a sulpur bearing B-vitamin. Biotin is one of the most widely known "beauty" vitamins. Biotin helps increase growth by contributing to the overal suphur content in out bodies and in aiding the breakdown of protein. Most people show improvement with a daily intake of atleast 5mg of Biotin. Some have taken up to 15 mg without adverse results. There are no know adverse reactions to large doses of Biotin. Some diabetics are prescribed "super" doses to help insulin issues. When taking Biotin it is usually more benefical to split up doses thoughout the day. Biotin sometimes has to be manipulated to see the growth results. One way to do this is to alternate brands. Pick two brands and alternate between them every other month. Another way to do this is buy your daily dose before bedtime. Sleeping on some water soluble vitamins sometimes helps with absorbtion. You can also do a "loading dose" with biotin. For example, lets say you desire an overall intake of 7mg. For the first four weeks you take 10 mg, then for two weeks you drop down to 5mg, and then stick to 7mg thereafter as your maintance dose.
B5 also helps thicken hair strands. You can also take this separately.
One thing to remember when taking indiviual b vitamins is that your body needs a balance of B-vitamins and just taking one by itself can throw off our balance. So if you are taking biotin or b5 by itself you might want to include a b-complex once a day if your multivitamin doesn't have alot. Also, when taking any sort of B-vitamin it is important to space out your doses and make sure you are consuming enough water. If you are sensitive to supplements, start on low doses and work your way up. Stop if you have any adverse side effects.