Major Depressive Disorder (MDD) is characterized by persistent and severe feelings of sadness, hopelessness, and a loss of interest or pleasure in most activities. It often includes symptoms like changes in appetite, sleep disturbances, fatigue, and difficulty concentrating.

Generalized Anxiety Disorder (GAD) involves excessive, uncontrollable worry and anxiety about various life events or activities. Physical symptoms like muscle tension, restlessness, and irritability are common.

Obsessive-Compulsive Disorder (OCD) is marked by the presence of obsessions (repetitive, intrusive, and unwanted thoughts) and compulsions (repetitive behaviors performed to alleviate anxiety caused by obsessions).

Post-Traumatic Stress Disorder (PTSD) occurs after experiencing or witnessing a traumatic event. Symptoms include flashbacks, nightmares, hypervigilance, and emotional numbness. It can severely impact daily functioning.

Bipolar I involves episodes of mania (elevated mood, increased energy) and major depressive episodes. Manic episodes may lead to impaired judgment and impulsive behavior.

Bipolar II features recurrent depressive episodes and hypomanic episodes (less severe than full mania). Hypomania may not cause significant impairment but can still affect functioning.

Schizophrenia is a severe mental disorder characterized by distorted thinking, hallucinations, delusions, disorganized speech, and impaired social and occupational functioning. It often involves a loss of touch with reality.

Schizoaffective disorder combines features of schizophrenia and mood disorders. Individuals experience both psychotic symptoms (hallucinations, delusions) and mood disturbances (depression or mania).

ADHD is characterized by persistent patterns of inattention, hyperactivity, and impulsivity. It often begins in childhood and can affect academic and occupational functioning.