Can Immunotherapy Cause Weight Gain and How to Manage It

Immunotherapy can be linked to weight changes, including weight gain, in some people. This often happens indirectly through hormone (endocrine) side effects such as thyroid, pituitary, or adrenal gland problems, which can cause weight gain or weight loss and other symptoms like fatigue and feeling cold. ^[1] These endocrine effects are recognized side effects of immune checkpoint therapies and should be monitored and treated early. ^[2] Weight loss is also commonly reported in clinical trials of checkpoint inhibitors like nivolumab, which shows that weight can change in both directions depending on the individual and context. ^[3]

Why Weight Gain Can Happen

• Endocrine (hormone) effects: Immunotherapy can inflame glands like the thyroid (leading to hypothyroidism), pituitary (hypophysitis), or adrenal glands; hypothyroidism, for example, can slow metabolism and contribute to weight gain, fatigue, hair loss, constipation, and feeling cold. ^[1] These hormone-related issues are among the most common immune-related side effects and need prompt evaluation and treatment. ^[4]
• Fatigue and lower activity: Immunotherapy can cause significant tiredness, which may reduce daily movement and calorie burn, contributing to gradual weight gain. ^[5]
• Appetite and coping changes: Changes in eating patterns during cancer treatment (more refined carbs, larger portions, sugary drinks) can lead to weight gain, especially when activity is down. ^{[6] [7]}
• Steroid medications: If steroids are used to treat immune-related side effects, they can increase appetite and cause fluid retention and weight gain, so careful monitoring is recommended. ^[8]

Red Flags That Need Medical Review

• New or worsening fatigue, feeling unusually cold, hair loss, constipation, mood changes, dizziness, or headache along with weight changes could signal a hormone issue from immunotherapy. ^[1] Report these promptly so your team can check labs (like TSH, free T4, cortisol). ^[2]
• Rapid, sudden weight gain, swelling in legs or shortness of breath while on steroids can indicate fluid retention and needs quick medical attention. ^[8]

Practical Steps to Cope With Weight Gain

• Ask for endocrine testing: If you notice weight gain with fatigue or cold intolerance, request thyroid and adrenal testing; treating hypothyroidism or adrenal issues can help normalize weight trends. ^{[1] [4]}
• Optimize daily activity: Gentle, regular movement helps counter fatigue and supports weight control; even short, frequent walks can help when energy is low. ^[5]
• Balance your plate: Aim for lean proteins, high-fiber vegetables, whole grains, and healthy fats while limiting sugary drinks and excess refined carbohydrates that can drive weight gain. ^[6]
• Watch portions and patterns: Plate your meals, slow your eating, and avoid grazing; these small habits can reduce unintentional extra calories during treatment. ^[6]
• Manage fatigue first: Improving sleep routines and pacing activities may reduce fatigue-driven overeating and inactivity. ^[5]
• Get nutrition support: A clinical dietitian can tailor strategies to your symptoms, preferences, and treatment plan to prevent unwanted weight gain. ^[6]
• Review steroid plans: If you must use steroids for immune side effects, discuss the lowest effective dose and shortest duration, and monitor weight and blood pressure regularly. ^[8]

When Weight Gain Might Be Expected or Variable

Weight changes during cancer therapy are common: some people gain weight due to fatigue and diet changes, while others lose weight due to appetite loss or gastrointestinal side effects. ^[9] Keeping weight as stable as possible is generally helpful, and early support makes a difference. ^[6]

Summary

• Immunotherapy can contribute to weight gain, often through hormone-related side effects that also cause fatigue, cold intolerance, and other symptoms. Early recognition and treatment are important. ^{[1] [2]}
• Practical steps endocrine evaluation, balanced nutrition, routine activity, portion awareness, fatigue management, and careful steroid use can help you manage weight safely during treatment. ^{[6] [8]}