Vitamin injections provide direct delivery of nutrients into the body’s tissues, ensuring 100% absorption of the active ingredients. Traditionally, vitamin B12 replacement has been administered intramuscularly because absorption through the gastrointestinal tract is deficient.

No First-Pass Metabolism
Once absorbed by the digestive system, oral supplements are heavily metabolized (broken down into their basic components) by gastrointestinal tissues and liver before being released into systemic circulation. This process, called first-pass metabolism, reduces the amount of active ingredients available to the body.
In contrast, vitamin injections avoid the first-pass effect. Consequently, the active ingredients are not subjected to the extensive metabolism encountered by oral supplements, resulting in higher levels of nutrients actually reaching their target tissues.

Rapid Onset of Action
Oral supplements must first undergo digestion, absorption and metabolism before any nutrients are released into the bloodstream. This process can take hours before the active ingredients start to become available to target tissues.
Unlike the oral route, the injectable administration of nutrients is a rapid method of dietary supplementation. Following the injection of vitamin supplements, the body can start to utilize the active ingredients immediately in order to correct dietary deficiencies.

Less Frequent Dosing
Because of low bioavailability and extensive metabolism, oral supplements must be dosed frequently to be effective while still not correcting micronutrient deficiencies. Depending on the brand, some supplements require the patient to take several pills per day.

Vitamin injections, on the other hand, are completely absorbed and avoid extensive metabolism, providing higher concentrations of nutrients available to target tissues. In addition, intramuscular injections create a depot effect in which the active ingredients are released progressively over time in a steady-state manner. Therefore, vitamin injections require less frequent dosing than oral supplements.