Recreational marijuana sales began on January 1 in California.

California, the nation’s most populous state, is the sixth state to allow sales of recreational marijuana.

Adults 21 and older can possess as much as one ounce of marijuana, and grow up to six plants at home.

The marijuana industry in California is forecast to reach $7 billion in a few years, the article notes. The entire U.S. legal marijuana market was worth $6.6 billion in 2016, according to New Frontier Data, which tracks the industry.

Marijuana remains illegal under federal law. It is unlawful to take the drug across state lines, mail it or bring it on a plane.