I do not use multi vitamins, because I dont think they are important. I take all my vitamins through food.
This story suggests high doses could lead to cancer, although the people in the studies took them orally, not up their arses.
http://www.nytimes.com/2013/06/09/opinion/sunday/dont-take-your-vitamins.html?_r=0In a study published in The New England Journal of Medicine in 1994, 29,000 Finnish men, all smokers, had been given daily vitamin E, beta carotene, both or a placebo. The study found that those who had taken beta carotene for five to eight years were more likely to die from lung cancer or heart disease.
Two years later the same journal published another study on vitamin supplements. In it, 18,000 people who were at an increased risk of lung cancer because of asbestos exposure or smoking received a combination of vitamin A and beta carotene, or a placebo. Investigators stopped the study when they found that the risk of death from lung cancer for those who took the vitamins was 46 percent higher.