People go to rehab for a wide range of reasons, from alcohol and drug addiction to recovery after a stroke, surgery, or traumatic injury. The word “rehab” covers two broad categories: substance use and behavioral health treatment, and physical rehabilitation for medical conditions. In both cases, the goal is structured, intensive care that helps someone regain function they’ve lost or break free from a pattern that’s harming their life.
Alcohol and Drug Addiction
Substance use disorders are the most commonly associated reason people enter rehab. Alcohol use disorder alone accounts for a massive share of treatment admissions. A person generally qualifies for a clinical diagnosis when they meet two or more of 11 criteria outlined in the standard psychiatric manual, which include things like drinking more than intended, failed attempts to cut back, cravings, and continued use despite relationship or health problems.
Opioid addiction, including prescription painkillers and illicit fentanyl, has driven a surge in rehab admissions over the past decade. Stimulants like methamphetamine and cocaine are also primary reasons people seek treatment. In 2011, SAMHSA data showed roughly 1.84 million admissions to substance abuse treatment programs in the United States. About two-thirds of those admissions were men, and one-third were women, a ratio that has remained fairly consistent across age groups.
Treatment programs range from outpatient counseling a few hours a week to 30-, 60-, or 90-day residential stays where the person lives at the facility. The level of care depends on how severe the addiction is, whether the person has a stable home environment, and whether they’ve relapsed after previous treatment attempts.
Mental Health and Dual Diagnosis
Many people who enter rehab for addiction are also dealing with a mental health condition like depression, anxiety, bipolar disorder, or PTSD. This combination is called a dual diagnosis or co-occurring disorder. In one large study of nearly 10,000 patients across inpatient and outpatient mental health programs, 18.5% had a co-occurring substance use and mental health disorder. That number likely understates reality, since many people aren’t screened for both conditions at the same time.
Some residential treatment programs focus primarily on mental health rather than addiction. These programs serve people whose depression, anxiety, trauma, or psychotic disorders have become severe enough that outpatient therapy and medication alone aren’t keeping them stable. A residential stay provides round-the-clock support, structured therapy sessions, and a controlled environment that removes the stressors of daily life while someone stabilizes.
Eating Disorders
Residential rehab is a common path for people with serious eating disorders. In a study of patients treated in residential care, about half of both adolescents and adults were diagnosed with a form of anorexia nervosa. For teens specifically, anorexia accounted for nearly 56% of admissions, while bulimia nervosa was the most frequent diagnosis among adults at 42.5%. Binge eating disorder and other less clearly defined eating patterns made up roughly 13% of admissions across both age groups.
Eating disorder rehab typically combines medical monitoring (since malnutrition and purging can cause dangerous heart and organ complications), structured meals, nutritional counseling, and intensive therapy to address the psychological drivers behind the disorder. Stays often last 30 to 90 days, though some people need longer depending on how medically compromised they are at admission.
Behavioral Addictions
Not all addiction involves a substance. Behavioral addictions follow the same cycle of compulsion, escalation, and withdrawal that drug and alcohol addiction do, just without a chemical substance. Gambling addiction is the most well-established and was the first behavioral addiction recognized with a formal psychiatric diagnosis. But residential treatment programs also exist for compulsive sexual behavior, internet and gaming addiction, compulsive overeating, and even pathological work habits.
People with behavioral addictions experience real withdrawal symptoms when they stop, including excessive fatigue, sleep disruption, irritability, and mood swings. Treatment mirrors substance use rehab in many ways: cognitive behavioral therapy, group support, identifying triggers, and building healthier coping strategies. These programs are less common than substance use treatment centers but have grown significantly as awareness of behavioral addiction has increased.
Physical Rehabilitation After Illness or Injury
The other major meaning of “rehab” is inpatient physical rehabilitation, which serves people recovering from serious medical events. The most common reasons for admission include stroke, spinal cord injury, traumatic brain injury, amputations, joint replacements, major trauma involving multiple body systems, cancer treatment complications, and neurological conditions like multiple sclerosis.
Inpatient physical rehab is intensive. Medicare covers it when a doctor certifies that the patient needs an intensive therapy program, continued medical supervision, and coordinated care across multiple providers. In practice, this means the person needs at least three hours of therapy per day (physical, occupational, or speech therapy depending on the condition) and has functional deficits significant enough that they can’t safely go home yet.
One notable gap: a multicenter study in Australia found that 37% of stroke patients were never even assessed for rehabilitation. This suggests that many people who could benefit from rehab after a stroke or similar event don’t get referred, often because of age, other medical conditions, or assumptions about their recovery potential.
Post-Surgical Recovery
Major orthopedic surgeries, particularly hip and knee replacements, are among the most frequent reasons people enter inpatient rehab. The determining factor is usually whether the person can safely perform basic daily tasks at home. Someone who lives alone, has limited mobility before surgery, or had complications during the procedure is more likely to need a rehab stay rather than going directly home with outpatient therapy.
A typical post-surgical rehab stay lasts one to three weeks. The focus is on regaining the ability to walk, climb stairs, get in and out of bed, and manage personal care independently. Patients work with physical and occupational therapists daily, and the facility coordinates pain management and wound care alongside the rehabilitation program. For many people, this structured environment makes the difference between a smooth recovery and a readmission to the hospital.