President Donald Trump has signed an executive order that will expand access to cannabis, a long anticipated move that would mark the most significant shift in US drug policy in decades.

The order directs the US attorney general to reclassify cannabis from a Schedule I narcotic to a Schedule III drug - placing it under the same category as Tylenol with codeine.

Cannabis will remain illegal at the federal level, but classifying it as a Schedule III narcotic would allow expanded research to be conducted into its potential benefits.

Several Republican lawmakers cautioned against the move, arguing it could normalize cannabis use.

The US Drug Enforcement Agency notes that Schedule III narcotics have only a 'moderate to low potential for physical and psychological dependence.'

Speaking in the Oval Office during the signing ceremony, Trump stated that people have been 'begging' for the change, especially those in 'great pain' due to various medical ailments.

In addition to the reclassification, Trump has ordered the White House to work with Congress to allow some Americans access to cannabidiol, commonly known as CBD.

While the reclassification is celebrated by many in the cannabis advocacy community, it has faced opposition from some Republican senators, who have expressed concerns about the health impacts of cannabis.

A recent Gallup poll reveals that a majority of Americans support legalization, suggesting an evolving public perception of cannabis use.

The cannabis industry is expected to benefit from new opportunities and awareness as a result of this significant policy shift.