When the substance or substances are absent, the brain loses its natural capacity to create pleasure of a feeling of well being. In the chemically altered brain, a profound interference in the ability to experience pleasure occurs, causing the user to feel dysphoria, anxiety, frustration and craving. Injury caused by insensitivity in pleasure centers causes the user to feel the opposite of the drug euphoria. Sobriety starts to feel the opposite of the euphoric drug-induced state. Sobriety starts to become associated with dysphoria and discomfort, and the drug-induced state can be perceived as the normal, balanced place to be.
Dual diagnosis is another important biological consideration.
If a person suffers from depression or anxiety, they may use substances to medicate uncomfortable feelings. For the dual-diagnosed, receiving psychiatric treatment with medication often helps stabilize one's baseline mood, which in turn facilitates recovery or sobriety. Tolerance of a substance is also a strong indicator of addiction. One needs increased amounts to get the same effect. Due to the social networks woven between users, substances often become a crucial part of one's identity and social fabric.