Oral vitamins travel through the digestive system which can result in negative side effects such as nausea and constipation, and only allows for 20-30% absorption. Vitamins and minerals administered intravenously guarantee 100% absorption into the bloodstream, and a much higher dose of vitamins can be tolerated. The results are therefore more effective and longer lasting. Even with Vitamin B12 injections, the Vitamins enter the muscle first, therefore you only get about a 60% absorption, and they are bloody sore! You need a course of four to six Vit B shots to be effective.