Indigo carmine only recently was found to have a vasopressor effect. Intravenous injection in anesthetized and unanesthetized patients resulted in blood pressure elevation and bradycardia. This effect appears analogous to that of serotonin which indigo carmine structurally resembles. This drug should be used with caution in patients with cardiovascular disease.
Wu, C. C. and Johnson, Arthur J.
"The Vasopressor Effect of Indigo Carmine,"
Henry Ford Hospital Medical Journal
: Vol. 17
Available at: https://scholarlycommons.henryford.com/hfhmedjournal/vol17/iss2/10