Substance abuse is a leading cause of new and long-term homelessness in Los Angeles. Substance abuse is defined as a disease that affects a person's brain and behavior and leads to an inability to control the use of a legal or illegal drug or medication. Substances such as alcohol, marijuana and nicotine also are considered drugs. When you're addicted, you may continue using the drug despite the harm it causes [a].

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Addictive substances are always banned from homeless shelters. While this is necessary, avid substance abusers who are unable or unwilling to get treatment will often opt to continue using without utilizing available shelters or rehabilitation centers. As it's often very easy for homeless persons to access said substances, usage is ongoing. In the United States, 35% of individuals living homeless have a substance abuse disorder [b].