Clinically severe obesity, or morbid obesity, can increase the risk of a range of health issues. A doctor may classify obesity as clinically severe if an adult has a body mass index (BMI) of 40 or above and a high percentage of body fat.

BMI is not a diagnostic tool, but it can indicate the risk of developing various health issues.

Having severe obesity can make it difficult to do everyday activities, such as walking, breathing, and sleeping. It can also increase the risk of cardiovascular disease, type 2 diabetes, and various other health conditions.

Severe obesity vs. morbid obesity

Although severe obesity used to be called morbid obesity, people are using this term less, as many consider it offensive. “Class 3 obesity” is another more acceptable way to refer to adults whose BMI falls within the range stated above.

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According to the National Institute of Diabetes and Digestive and Kidney Diseases, around 1 in 13 people in the United States had severe obesity during 2013–2014.

Below, learn more about what clinically severe obesity is and which treatments are available.

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The term “morbid obesity” originated in 1963 by two healthcare professionals who were trying to find a way to get insurance reimbursement for intestinal bypass surgery for people who were severely overweight.

By using the word “morbid,” which in a medical setting means illness or disease, they hoped to make a case for surgery for those with a BMI of 40 or higher. BMI is a scale that helps medical professionals tell whether a person has a risk of developing certain health conditions.

The following chart shows different classifications of BMI:

under 18.5underweight
18.5 to less than 25moderate weight
25 to less than 30overweight
30 to less than 35class 1 obesity
35 to less than 40class 2 obesity
above 40class 3 obesity

Find a BMI calculator and more information about BMI.

A person with obesity has a greater risk of heart disease and other conditions. The higher the class of obesity, the greater the likelihood of developing these complications.

However, it is worth noting that a person’s BMI does not necessarily indicate whether they have a healthy weight. It does not reflect the percentage of muscle mass compared with the percentage of fat in the body.

How useful is BMI as a tool for measuring weight and health?

Checking a person’s waist-to-hip ratio and the distribution of fat in their body can give a better idea of their risk of developing complications. Scientists have linked a high waist circumference due to body fat with a greater risk of cardiovascular disease.

The complications of obesity can include:

These conditions can affect a person’s life expectancy and quality of life.

Certain factors can influence the risk of developing any class of obesity:

  • Dietary habits and activity levels can affect a person’s levels of energy.
  • Socioeconomic conditions can limit access to fresh food and the ability to exercise.
  • Genetic factors may predispose a person to obesity.
  • Family history may contribute through both genetic and environmental factors.
  • Some medical conditions have links with obesity, including Cushing’s syndrome and polycystic ovary syndrome.
  • Stress and anxiety can increase levels of the hormone cortisol, which can affect fat storage and weight gain.
  • A lack of sleep may contribute.

Do social factors affect the risk of obesity?

The authors of a 2017 review of studies from around the world suggest that the following social factors, among others, may play a role:

  • stress due to trauma, relationship problems, financial difficulties, or a combination
  • levels of health and dietary awareness
  • workplace settings, including working hours and the likelihood of eating takeout
  • access to and availability of healthy food
  • access to green space and other considerations involving urban living and activity levels

According to the Centers for Disease Control and Prevention (CDC), obesity affects around 49.6% of Black adults, 44.8% of Hispanic adults, and 42.2% of white adults in the United States.

However, a 2017 survey published by the CDC reveals a more nuanced picture, indicating that the prevalence of obesity varies according to combinations of factors such as education level, income, gender, and race. The relationships among these factors appear complex.

A person with obesity may experience:

  • sweating
  • tiredness
  • joint and back pain
  • difficulty breathing
  • sleep problems, including snoring
  • difficulty with physical activity
  • low confidence and feelings of isolation
  • high blood pressure and other symptoms of metabolic syndrome
  • symptoms of other complications, which we describe below

Indications of severe obesity include:

If a person visits their doctor with concerns about their weight or BMI, the doctor will likely:

  • measure their weight and height to confirm their BMI
  • ask about dietary and exercise habits
  • consider the person’s individual and family medical histories
  • do blood tests to look for health conditions that may underlie obesity
  • test for complications that may need medical attention, such as high blood pressure

If a person has severe obesity or complications relating to it, a doctor may:

  • recommend an appropriate weight loss plan
  • work with the person to develop an exercise plan
  • recommend a physical therapy plan if the person has limited mobility
  • prescribe medication
  • recommend bariatric surgery if other options do not help
  • address any complications, such as type 2 diabetes and other features of metabolic syndrome

It is best to work with a doctor or nutritionist to develop a suitable plan and follow the instructions carefully. Losing weight too rapidly or starting vigorous exercise too quickly can have negative effects.


There are a number of weight loss medications available to treat severe obesity. Doctors now have a range of prescription medications used to manage this medical condition. These include:

  • Semaglutide (Wegovy): an injection that decreases glucagon and works by helping the pancreas to release the right amount of insulin when blood sugar levels are high so that sugar can be used for energy
  • Liraglutide (Saxenda): an injectable medication that, like semaglutide, works by increasing the release of insulin from the pancreas and decreasing excessive glucagon release
  • Setmelanotide (IMCIVREE): an injectable medication used for weight management in people with certain genetic conditions
  • Phentermine-topiramate (Qsymia): an appetite-suppressing drug for short-term treatment of obesity
  • Orlistat (Xenical): an oral medication that blocks the enzyme that breaks down fats in your diet so fats are passed through the body in a bowel movement
  • Bupropion-naltrexone (Contrave): a fixed-dose combination medication for treating chronic obesity

A person should work closely with their doctor to find the right combination of treatments, as weight loss drugs alone are not the solution.

Diet, exercise, and lifestyle changes may be necessary in conjunction with taking a prescribed medication, especially as certain medications, such as semaglutide and liraglutide, reduce appetite and slow the emptying of the stomach.

Surgical options

If dietary changes, lifestyle changes, and medications do not help, a person’s doctor may recommend surgery. Some of these procedures include:

  • gastric banding, in which a surgeon places a ring around the stomach, limiting the amount of food that can enter
  • gastric bypass, which aims to increase the feeling of fullness and lead to the absorption of fewer calories
  • sleeve gastrectomy, in which the surgeon removes part of the stomach
  • intragastric balloon, a temporary measure in which the surgeon places a balloon in the stomach to take up space

If a person loses a significant amount of weight, they may have unwanted folds of skin. Surgery can also address this.

Find out more about treatments for obesity.

There is no single way to lose weight or prevent weight gain. The best option will depend on the individual. However, dietary strategies and exercise can help.

Dietary tips can include:

  • consuming plenty of fresh fruits and vegetables
  • favoring whole or unprocessed foods
  • avoiding trans fats and saturated fats and opting for healthy fats, such as from safflower or corn oils
  • limiting the intake of sugar and sweetened foods
  • monitoring the caloric intake, if a healthcare professional recommends this
  • using a smaller plate
  • eating only at regular times
  • eating more slowly
  • avoiding triggers and habits that lead to overeating, such as having some cake with coffee at break times

Current guidelines recommend that, when possible, adults get at least 150 minutes of moderate-intensity activity a week. This could include walking, swimming, or cycling, for example. It might involve 10-minute sessions several times a day on most days of the week.

A doctor can advise on how much and what type of exercise a person should do, depending on their overall health, age, and other factors.

How can walking help a person lose weight?

Severe obesity is not an illness, but it can increase the risk of a wide range of health conditions, some of which can be life threatening. In most cases, severe obesity is reversible.

Anyone with concerns about obesity or its possible symptoms should receive medical advice. Treatments can enable a person to adjust their weight and may help prevent potentially serious complications.