1. First: determine if there is an acute problem

• Airway or breathing difficulty, hypoxaemia, obesity-hypoventilation syndrome, severe obstructive sleep apnoea
• Chest pain, acute heart failure, venous thromboembolism
• Severe hypertension or uncontrolled diabetes
• Immobility, cellulitis, pressure injury, severe joint pain
• Suicidality, severe depression, binge-eating disorder, or an eating disorder

2. Confirm and stage adiposity and risk

• Measure height, weight, and BMI.
  • Class I: 30.0-34.9 kg/m²
  • Class II: 35.0-39.9 kg/m²
  • Class III (severe obesity): ≥40 kg/m²
• Measure waist circumference or waist-to-height ratio where useful. For those with BMI ≥35 kg/m², the BMI and complication burden usually drive risk assessment more than waist size.
• Record blood pressure using an appropriate large cuff.
• Establish trajectory: lifelong pattern, recent rapid gain, prior highest/lowest weights, previous efforts and responses.

3. Take an obesity-focused history

Causes and contributors

• Dietary pattern: portion size, ultra-processed foods, sugary drinks, alcohol, night eating, binge eating
• Physical activity, mobility limitations, pain, occupation, sedentary time
• Sleep duration and quality, snoring, witnessed apnoeas, daytime somnolence
• Stress, trauma, depression, anxiety, social isolation, finances, food insecurity
• Family history and life events associated with weight gain
• Pregnancy, menstrual irregularity, infertility, hirsutism suggesting PCOS where relevant

Medication review

• Insulin, sulfonylureas, thiazolidinediones
• Glucocorticoids
• Antipsychotics, especially olanzapine and clozapine
• Some antidepressants, mood stabilisers, and antiseizure medicines

Screen for secondary causes, selectively

• Hypothyroidism
• Cushing syndrome
• PCOS
• Hypothalamic disease
• Medication-induced gain

Establish goals and readiness

4. Examine for complications

• BP, pulse, oxygen saturation
• Signs of insulin resistance: acanthosis nigricans
• Cardiovascular examination and peripheral oedema
• Respiratory examination, neck circumference, features of sleep apnoea or hypoventilation
• Abdomen: hepatomegaly, hernia, skin-fold infection
• Lower limbs: venous disease, lymphoedema, ulcers
• Musculoskeletal function: osteoarthritis, gait, mobility
• Skin: intertrigo, pressure injury
• Endocrine clues: hirsutism, Cushingoid appearance

5. Screen for obesity-related disease

6. Investigations

• HbA1c or fasting plasma glucose
• Fasting lipid profile
• Renal function, electrolytes, liver enzymes
• Thyroid function if symptoms/signs or unexplained weight change
• Urinalysis where indicated
• ECG if cardiovascular symptoms/risk or before surgery
• Sleep study referral if OSA is suspected
• Pregnancy test before weight-loss medicines when relevant

7. Start chronic disease management

Foundation for everyone

• Individualised calorie reduction that remains nutritionally adequate
• Dietitian support when possible
• Gradual activity plan matched to mobility and cardiorespiratory status
• Resistance training and reduction in sedentary time
• Behavioural strategies: self-monitoring, problem solving, relapse planning, sleep and stress management
• Psychological care and eating-disorder treatment when indicated

Pharmacotherapy

• Review contraindications, pregnancy plans, renal/hepatic status, pancreatitis/gallbladder history, psychiatric history, and interacting medicines.
• Explain that pharmacotherapy is often long term and stopping it commonly leads to weight regain.
• Monitor weight, adverse effects, glycaemia, BP, and medication adherence.

Metabolic/bariatric surgery referral

8. Follow-up plan

• Weight and waist measure when appropriate
• BP, HbA1c/glucose, lipids, liver markers
• Sleep symptoms, mobility, pain, mood, eating behaviours
• Medication adverse effects and adherence
• Patient-selected functional outcomes, not weight alone

Latest adult obesity pharmacotherapy guidelines

1. United States: ACP Living Clinical Guideline, April 2026

• For nonpregnant adults with BMI ≥30 kg/m², pharmacotherapy plus lifestyle modification is suggested.
• For BMI 27 to <30 kg/m², medication is suggested when at least one complication is present: type 2 diabetes, dyslipidaemia, hypertension, OSA, or cardiovascular disease.
• Preferred first-line medicines: semaglutide or tirzepatide.
• ACP ranks phentermine-topiramate second line, liraglutide third line, and naltrexone-bupropion fourth line.
• Choice should incorporate expected benefit, harms, cost and access, comorbidities, contraindications, patient goals and preferences, including pregnancy plans.

2. United States: TOS/OMA/OAC GRADE guidance, 2026

• Strong recommendations: semaglutide, tirzepatide, naltrexone-bupropion, and setmelanotide when clinically indicated.
• Conditional recommendations: orlistat, phentermine, phentermine-topiramate, liraglutide, and selected complication-specific uses.
• Strongly recommends continuing an effective medication for weight-loss maintenance, recognizing obesity as a chronic, relapsing condition.

3. WHO GLP-1 guideline, 2026

4. EASO pharmacological framework, 2026

• Type 2 diabetes/prediabetes: tirzepatide or semaglutide first choice.
• Established cardiovascular disease: semaglutide has the clearest cardiovascular-outcome evidence.
• OSA: tirzepatide is favored where indicated.
• Knee osteoarthritis: semaglutide is favored where pain reduction is the primary target.
• MASH: incretin-based treatment is increasingly supported, with evidence evolving rapidly.

5. Canadian Adult Obesity CPG update, 2025

• Offer medication with health-behaviour treatment for BMI ≥30 kg/m², or BMI ≥27 kg/m² plus an adiposity-related complication.
• Individualize selection using central adiposity, complications, preferences, safety, affordability and long-term adherence.
• Recommended agents include:
  • Semaglutide 2.4 mg weekly
  • Tirzepatide 5, 10, or 15 mg weekly
  • Liraglutide 3 mg daily
  • Naltrexone-bupropion 16/180 mg twice daily
  • Orlistat 120 mg three times daily
• Continue effective therapy long term to prevent weight regain.
• Recommends against compounded obesity medicines and against use of drugs not approved for weight management solely for weight loss.

6. United Kingdom: NICE NG246, 2025

Practical consensus across current guidelines

1. Medication is adjunctive, not standalone: prescribe with nutrition, activity, behavioural, and complication management.
2. Semaglutide and tirzepatide are generally preferred where available and suitable, because they produce the greatest average weight loss and have outcome benefits in selected comorbidities.
3. Treat long term if effective and tolerated. Discontinuation commonly causes weight regain.
4. Select treatment by complication profile, not BMI alone.
5. Avoid in pregnancy and assess contraindications, adverse effects, drug interactions, cost, access and patient preference.
6. Refer for metabolic/bariatric surgery assessment when indicated, particularly in severe obesity or inadequately controlled obesity-related disease.

Referral for metabolic/bariatric surgery

Who to refer

Current ASMBS/IFSO criteria

• BMI ≥35 kg/m², regardless of whether obesity-related complications are present.
• Type 2 diabetes with BMI ≥30 kg/m².
• BMI 30-34.9 kg/m² with inadequate durable weight loss or insufficient improvement of obesity-related complications despite non-surgical care.

Refer promptly when severe complications are present

• Poorly controlled type 2 diabetes, especially with escalating medication needs
• Moderate-to-severe obstructive sleep apnoea or obesity-hypoventilation syndrome
• Hypertension, established cardiovascular disease, or heart failure
• Metabolic dysfunction-associated steatotic liver disease or MASH
• Severe osteoarthritis, impaired mobility, or major functional limitation
• Idiopathic intracranial hypertension
• Infertility/PCOS where excess adiposity is a major contributor
• Severe GERD or other obesity-related disease, noting that procedure choice requires specialist input

What to include in the referral

1. Anthropometry
   • Height, weight, BMI, trend in weight and highest adult weight
   • Waist measurement if available
2. Obesity history
   • Duration and trajectory of weight gain
   • Previous nutrition, activity, behavioural and medication interventions, including outcomes and adverse effects
   • Current anti-obesity medicines and other drugs that promote weight gain
3. Comorbidities and investigations
   • Type 2 diabetes/prediabetes: HbA1c and treatment
   • BP, lipid profile, renal and liver function
   • OSA screening or sleep-study result, CPAP use
   • Cardiac disease, VTE history, mobility limitations
   • GERD, liver disease, gallstone disease
   • Reproductive plans and contraceptive requirements where relevant
4. Psychosocial assessment
   • Depression, suicidality, psychosis, bipolar disorder stability
   • Binge eating or other eating disorder
   • Alcohol, tobacco, and substance use
   • Capacity, social support, housing/food security, ability to attend lifelong follow-up
5. Patient goals
   • What outcome matters most: diabetes improvement, mobility, OSA, pain, fertility, quality of life, or weight loss.
   • Document informed willingness to engage with postoperative diet, supplements, monitoring, and follow-up.

Important points before referral

• Do not require patients to achieve arbitrary preoperative weight loss before referral. A specialist team can determine readiness and optimize risk.
• A mental-health condition is not automatically a reason to deny referral. It needs appropriate assessment and treatment. Active untreated psychosis, uncontrolled substance use, recent severe suicidal depression, or inability to follow postoperative care may require stabilization first.
• Smoking cessation and optimization of diabetes, OSA, cardiopulmonary disease, nutrition, and anaesthetic risk should happen in parallel with referral.
• Pregnancy is usually a reason to defer surgery. Patients should receive preconception counselling and a plan to avoid pregnancy during the rapid weight-loss period after surgery.

Suggested referral wording

Please assess this patient for metabolic/bariatric surgery. They have a BMI of __ kg/m² and obesity-related complications including __. They have undertaken __ interventions, with __ response. Relevant investigations: HbA1c __, BP __, lipids __, liver tests __, sleep-study/OSA status __. Current medicines include __. They understand that surgery requires lifelong nutritional supplementation and follow-up and wish to explore this option.

Why referral is appropriate

• BMI >50 kg/m² is class III severe obesity and substantially exceeds current ASMBS/IFSO referral criteria of BMI ≥35 kg/m² regardless of comorbidities.
• MASLD is an additional obesity-related complication and commonly improves after sustained surgical weight loss.
• Diabetes, hypertension, or established cardiovascular disease are not prerequisites at this BMI. They should be actively screened for, but their absence does not reduce eligibility for assessment.

Concurrent work-up before or alongside referral

1. Stage liver disease
   • Liver panel, platelet count, albumin, INR, bilirubin
   • Calculate FIB-4
   • Perform transient elastography or refer to hepatology if FIB-4 is elevated/indeterminate, elastography suggests advanced fibrosis, or there are signs of cirrhosis.
2. Exclude advanced liver disease and portal hypertension
   • Decompensated cirrhosis, portal hypertension, ascites, varices, encephalopathy, or impaired synthetic function require hepatology-led assessment.
   • Bariatric surgery in decompensated cirrhosis or portal hypertension carries increased mortality and should only be considered in highly specialized high-volume centres, often integrated with transplant expertise. Harrison’s Principles of Internal Medicine 22E, Treatment of MASLD.
3. Screen for unrecognized complications
   • HbA1c/fasting glucose, BP, lipids
   • OSA screening and sleep study when clinically indicated
   • Renal function, mobility and joint disease, mental health, alcohol/substance use, eating disorder assessment.
4. Start treatment now
   • Structured nutrition and activity support.
   • Discuss anti-obesity pharmacotherapy, especially semaglutide or tirzepatide if appropriate and locally accessible. This can be used while awaiting surgical assessment and does not preclude surgery.

Suggested referral note

Please assess for metabolic/bariatric surgery. Patient has class III severe obesity with BMI __ kg/m² (>50 kg/m²) and MASLD. No known type 2 diabetes or established cardiovascular disease. Previous weight-management interventions: __. Liver staging: ALT/AST __, platelets __, FIB-4 __, elastography __. OSA screen/study: __. Current medicines and psychosocial assessment: __. Patient understands the need for lifelong nutritional monitoring and wishes to explore surgical treatment.