Marijuana Justice Act of 2018 This bill amends the Controlled Substances Act: to remove marijuana and tetrahydrocannabinols from schedule I; and to eliminate criminal penalties for an individual who imports, exports, manufactures, distributes, or possesses with intent to distribute marijuana. It prohibits and reduces certain federal funds for a state without a statute legalizing marijuana, if the Bureau of Justice Assistance determines that such a state has a disproportionate arrest rate or disproportionate incarceration rate for marijuana offenses. The bill directs federal courts to expunge convictions for marijuana use or possession. Finally, it establishes in the Treasury the Community Reinvestment Fund. Amounts in the fund may be used by the Department of Housing and Urban Development to establish a grant program to reinvest in communities most affected by the war on drugs.