Iowa Gov. Kim Reynolds (R) has vetoed legislation that would have allowed medical marijuana products made and sold in the state to include more potency.

Reynolds wrote in a letter Friday that she opposed the bill because the state's medical marijuana board, made up largely of physicians, suggested the potency changes not be so broad.

Currently, the state's program allows for cannabidiol or CBD products with a 3 percent limit on THC — the chemical that gives users a high.

The vetoed bill would have created a new measurement system that limits users to 25 grams of THC per 90-day period.

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"Unfortunately, the bill would also remove the three percent limit on THC in medical CBD products and replace it with a limit of 25 grams of THC per 90-day period. This change was not recommended by the Board," Reynolds said.

“Ultimately, I believe Iowa must proceed cautiously to ensure that any expansion of our medical [cannabidiol] program is thoughtful and deliberate — particularly because Iowa’s program is in its infancy and the body of research that analyzes the efficacy of medical CBD is limited," Reynolds concluded.

The decision comes as many other states, such as California, Washington, Oregon and Maine, expand medical and recreational marijuana laws, and 2020 Democratic candidates talk of making it legal at the federal level.

A recent Hill-HarrisX poll showed 84 percent of Americans support legalizing marijuana.