Hemp, which is a variety of the Cannabis sativa plant, was banned in the United States along with marijuana in the 1930s. The main reason for the ban was the association of hemp with marijuana, which was being targeted as a drug with dangerous and addictive properties.

Hemp and marijuana are both varieties of the cannabis plant, and they look very similar, which made it difficult to differentiate between the two. They also have similar chemical compounds, including THC (tetrahydrocannabinol), the psychoactive compound that causes the "high" associated with marijuana use.

Another reason for the ban of hemp is that it was considered a major competitor to the timber, cotton, and synthetic-fiber industries. The Marihuana Tax Act of 1937 effectively made it too costly and burdensome for farmers to grow hemp, and it was banned along with marijuana.

In recent years, there has been a renewed interest in hemp as a crop for its uses in products such as paper, textiles, biofuel, and food. In 2018, the U.S. Congress passed the Farm Bill which legalizes hemp production, and the FDA has approved CBD derived from hemp as a dietary supplement. Today, hemp is grown in many states across the country, but it's still heavily regulated and it is illegal to grow hemp in some states.