The authors of a new study say one of the main methods of executing inmates in the United States, lethal injection, does not guarantee a fast or painless death.

U.S. researchers at the University of Miami and Fordham University say the anesthesia in the triple-drug cocktail used in U.S. executions is not always adjusted for body weight, so it may not always work well enough to block sensations caused by the other two drugs. They say prisoners may feel themselves choking to death, from a muscle-paralyzing drug, or feel a burning sensation as a third drug stops the heart.

At least 11 U.S. states have suspended execution by lethal injection over concerns about its effectiveness and proper administration. A number of states had turned to lethal injection, intending for it to be a more humane alternative to electrocution or gas chambers.

The journal publishing the findings, PLoS Medicine, also published an editorial calling for abolition of lethal-injection executions.

Supporters of the death penalty dismissed the findings as based on faulty assumptions.