The use of IV therapy in hospitals and emergency settings is a well-known, widespread practice since the 1930s. The majority of emergency medicine physicians use intravenous fluids in their treatment of intoxicated patients: link
IV Hydration with Vitamins is a wellness therapy; broad scientific conclusions beyond hydration and vitamin delivery for the general population are mixed, yet anecdotal claims are abundant. As with all medical procedures, results may vary as everyone's body is unique. Although research continues to be undertaken, there are an array of strong studies where IV therapy was used to help treat specific concerns.
For example, after a double-blind randomized controlled clinical trial, Suh et al. found that intravenous vitamin C administration reduces fatigue in office workers: link
In the summer of 2020, due to the Covid pandemic, Hiedra et al. noted a significant decrease in inflammatory markers, including ferritin and D-dimer, and a trend to decreasing FiO2 requirements, after intravenous administration of vitamin C: link
In Athletes, administration of saline IV resulted in greater fluid retention compared with oral and lower levels of fluid regulatory and stress hormones compared with both oral conditions: link
In a randomized clinical trial, Doig et al. concluded that amino acid IV therapy significantly improved kidney function in critically ill patients: link
Fischer et al. looked into intravenous administration of magnesium on complex regional pain syndrome in a randomized double‐blind placebo‐controlled trial, and realized there was significant improvement on some markers: link
Intravenous vitamin C has been researched for the treatment of illness. Padayatty et al. found that administering the maximum tolerated dose of vitamin C through IV therapy produces plasma levels 25 times that achieved when the same dose is administered orally: link
Gaffar Billoo et al. also looked into vitamin D deficiencies in children and concluded that injectable forms of vitamin D was shown better efficiency, which was statistically significant: link