Can immunotherapy cause mood swings?

Yes, mood swings and other changes in mood or behavior can occur with cancer immunotherapy, and they often stem from immune-related effects on hormone-producing glands (like the thyroid, pituitary, or adrenal glands). These endocrine side effects can lead to symptoms such as irritability, low sex drive, forgetfulness, feeling unusually cold, fatigue, weight changes, and dizziness, which may present as mood changes. ^[1] Mood or behavior changes can also be part of rare but serious nervous system inflammation (meningitis or encephalitis), which can include headaches, fever, confusion, memory problems, and hallucinations. ^[2]

Why mood changes happen

• Endocrine (hormonal) problems: Immunotherapy can inflame the thyroid, pituitary, adrenal glands, or pancreas, disrupting hormones that regulate energy, temperature, stress response, and mood. This disruption can trigger irritability, emotional lability, fatigue, weight change, and cognitive slip-ups. ^{[1] [3]}
• Neurologic inflammation (rare): Inflammation of the brain or its lining can cause confusion, memory changes, severe headaches, light sensitivity, and sometimes hallucinations, which can look like abrupt mood or behavior changes and requires urgent care. ^[2]
• Broader cognitive effects: Some treatments, including immunotherapy, can contribute to cognitive changes (attention, memory), which may feel like mood disturbance or increase frustration and anxiety. ^[4]

Red flags that need urgent attention

Seek prompt medical advice or go to emergency care if mood changes are accompanied by any of the following: persistent or severe headache, fever, confusion, worsening memory problems, new hallucinations, severe muscle weakness, extreme light sensitivity, fainting, or neck stiffness. These can signal serious neurologic side effects that need immediate evaluation. ^[2]

How clinicians evaluate it

• Symptom review and timing relative to infusions to see if patterns fit immune-related side effects. ^[5]
• Lab tests: Thyroid function (TSH, free T4), cortisol/ACTH for adrenal function, and other endocrine panels if indicated, because hormone disturbances are a common, treatable cause of mood symptoms on immunotherapy. ^{[1] [3]}
• Neurologic assessment if red flags are present, with imaging or lumbar puncture as guided by the care team. ^[2]

Practical coping strategies

• Tell your care team early: Most immunotherapy side effects can be managed safely if addressed early; waiting may allow them to worsen. ^{[6] [5]}
• Treat the cause: If tests show thyroiditis or adrenal insufficiency, replacing hormones (for example, thyroid hormone or steroids as directed by your oncology team) can relieve mood symptoms. ^{[1] [7] [8]}
• Manage depression and anxiety proactively: Report persistent low mood, loss of interest, sleep or appetite changes, or feelings that interfere with daily life; timely support and treatment can help. ^[9]
• Support your brain health: Cognitive strategies, rest, pacing, and minimizing multitasking can help with attention and memory changes linked to treatment. ^[4]
• Lean on support: Talk with trusted people, join support groups, or seek counseling; this can soften stress and improve coping during treatment. ^[10]

Step-by-step action plan

1. Track symptoms: Note when mood changes occur, their severity, any triggers, and associated symptoms (headache, fever, fatigue, cold intolerance). Bring this log to appointments. ^[5]
2. Call your oncology team: Ask about checking thyroid and adrenal function and reviewing your overall side effect profile, since hormone issues are a common, fixable cause. ^{[1] [3]}
3. Ask about treatment adjustments: Short-term steroid treatment or holding immunotherapy temporarily is sometimes used to control immune-related side effects when appropriate and guided by your care team. ^{[11] [12]}
4. Use mental health resources: If mood symptoms last 2 weeks or longer or you have thoughts of self-harm, contact your team immediately for evaluation and support services. ^[9]
5. Build daily routines: Gentle activity, regular sleep-wake times, balanced meals, hydration, and relaxation techniques (breathing, mindfulness) can stabilize energy and mood during treatment. ^[10]

Summary

• Mood swings can happen with immunotherapy, commonly due to immune-related hormone problems involving the thyroid, pituitary, or adrenal glands. Early reporting and simple blood tests often identify treatable causes. ^{[1] [3]}
• Rarely, serious brain inflammation can present with mood or behavior changes plus neurologic symptoms and needs urgent care. ^[2]
• Working closely with your care team, addressing hormone issues, and using mental health and supportive strategies usually helps manage these symptoms effectively. ^{[6] [9] [10]}

Quick reference table

Issue	Typical signs	Why it matters	What to do
Thyroid problems	Fatigue, feeling cold, hair loss, weight change, irritability, forgetfulness	Common immune-related cause of mood changes	Request TSH/free T4; treat if abnormal; monitor symptoms [1] [3]
Adrenal/pituitary issues	Dizziness/fainting, extreme tiredness, mood or behavior change, weight change	Can cause significant mood and energy shifts	Check morning cortisol/ACTH; follow team guidance on replacement or steroids [1] [3]
Neurologic inflammation (rare)	Headache, fever, confusion, memory problems, hallucinations, neck stiffness, light sensitivity	Medical emergency risk	Seek urgent care; follow neurologic workup and treatment [2]
Persistent depression/anxiety	Low mood >2 weeks, loss of interest, sleep/appetite change, restlessness	Treatable; affects quality of life and adherence	Notify team; consider counseling/medications/support services [9]
General side effects	Early mild symptoms that can worsen	Early action prevents complications	Report promptly; follow team plan [6] [5]