Oral vitamin supplement production is not regulated by the FDA whereas vitamins compounded for IV (intravenous) and IM (Intramuscular) use are heavily regulated. Only when a pill is deemed harmful by the FDA, after a lengthy process, it is removed from shelves.
When vitamins are administered intravenously or intramuscularly they bypass gastrointestinal metabolism. Oral vitamin supplements must first filter through your digestive system and provide only 20-30% absorption. When vitamins are ingested in tablet or capsule form, the contained micronutrients must disintegrate rather quickly and be released into the body within a 20 minute time period for any real efficacy. Delivering vitamins directly into the bloodstream or muscles provides increased bioavailability. Bioavailability is the degree and rate at which vitamins are absorbed by the body’s circulatory system and able to be effective.
Many over the counter supplements contain excipients, binders, fillers, and flow agents that can be used to make the ingredients stick together, mass produce in bulk, or allow formulas to run smoothly through manufacturers’ machines. In turn, all of such factors can contribute to the poor quality and disintegration rates for pills.