The main difference between marijuana and hemp is in the chemistry. Tetrahydrocannabinol (THC) in marijuana is the part that is responsible for the psychological effects. In the artwork above  the yellow highlight is there so you can see the difference in the chemistry. That one atom difference is why cannabidiol (CBD) or hemp, does not have the psychological effect. The average batch of marijuana contains 5% to 20% of THC. Hemp on the other hand, contains less than 0.3% of THC. Hemp is loaded with proteins, fiber, amino acids, vitamins, minerals, and fatty acids making it one of the best plant sources of protein.