Starting in 2013, Colorado legalized cannabis usage. In 2020, 34 states have legalized use of medical cannabis, and the 11 other states and Washington DC allow recreational cannabis usage.

Many people have argued that cannabis legalization will increase a state's GDP. One piece of evidence was that in Colorado, when recreational cannabis usage was legalized in 2013, Colorado's GDP increased by 5.4 percent while the US GDP growth was 1.8 percent.

How does cannabis legalization increase GDP? Explain succinctly with the GDP calculation in mind. Do not use unnecessary information.