Mood Swings: What Could Be Causing Them and When to Get Help

The Hormonal Axis: Why Hormones Are the First Place to Look

Hormones regulate neurotransmitter synthesis, receptor sensitivity, and neural circuit excitability. When levels shift abruptly or fall outside physiologic range, the brain's emotional regulation circuitry responds.

Estrogen modulates serotonin and dopamine activity in the prefrontal cortex and amygdala. A rapid drop in estradiol, as occurs premenstrually or during perimenopause, reduces serotonin transporter binding and destabilizes mood within days 1. Progesterone metabolites (particularly allopregnanolone) act on GABA-A receptors. When progesterone withdraws cyclically, the calming effect of GABAergic tone drops, producing anxiety, irritability, and emotional lability 2.

Testosterone influences mood in both sexes. The Endocrine Society's 2018 clinical practice guideline identifies "depressed mood, fatigue, and irritability" as symptoms warranting testosterone evaluation when total testosterone falls below 300 ng/dL 3. In men over 45, the Testosterone Trials (TTrials, N=790) demonstrated that testosterone gel improved mood scores on the PHQ-9 by 2.2 points compared to placebo at 12 months 4.

The takeaway is direct. If mood swings appeared alongside other hormonal symptoms (changes in menstrual pattern, fatigue, libido changes, weight shifts), a hormonal panel is the correct first step.

Thyroid Dysfunction: The Most Commonly Missed Cause

Thyroid hormones set the metabolic pace of every cell in the body, including neurons. Both hypothyroidism and hyperthyroidism produce mood disturbance, but they do so differently.

Hypothyroidism slows neural processing. A 2018 meta-analysis of 19 studies (N=36,174) found that subclinical hypothyroidism (TSH 4.5 to 10 mIU/L with normal free T4) was associated with a 2.3-fold increased risk of depression and a 2.1-fold increased risk of anxiety 5. Patients describe feeling "flat" most of the time with episodic irritability, a pattern frequently misread as depressive disorder.

Hyperthyroidism, by contrast, overstimulates the nervous system. Anxiety, emotional volatility, rapid cycling between agitation and tearfulness, and insomnia are hallmark features. Graves' disease (the most common cause of hyperthyroidism) affects roughly 1 in 200 people in the United States 6.

Dr. Antonio Bianco, past president of the American Thyroid Association, has noted: "Mood and cognitive complaints are among the earliest symptoms patients report, often months before the classic physical signs of thyroid disease become apparent" 7.

A simple TSH plus free T4 screen catches 95% of thyroid disorders. If TSH is abnormal, the next steps are free T3 and thyroid antibody testing (anti-TPO, TSI). Treatment with levothyroxine for hypothyroidism or methimazole for hyperthyroidism typically improves mood within 4 to 8 weeks.

Blood Sugar Dysregulation and Emotional Volatility

Reactive hypoglycemia and insulin resistance both create neurochemical conditions that mimic or worsen mood swings. The brain consumes roughly 20% of the body's glucose supply. When blood glucose drops below 70 mg/dL, the hypothalamic-pituitary-adrenal (HPA) axis triggers a counter-regulatory hormone surge: epinephrine, cortisol, and glucagon spike simultaneously 8.

That surge explains the sudden anxiety, irritability, heart pounding, and emotional fragility that patients describe 2 to 4 hours after a high-glycemic meal. This is not a psychiatric symptom. It is a metabolic event.

Insulin resistance compounds the problem. A 2019 study in Molecular Psychiatry (N=3,745) found that higher HOMA-IR (a marker of insulin resistance) was independently associated with increased depressive symptoms, even after adjusting for BMI and physical activity 9. The mechanism involves impaired glucose transport across the blood-brain barrier and downstream reductions in brain-derived neurotrophic factor (BDNF).

The diagnostic approach is straightforward. Fasting glucose, fasting insulin, and HbA1c form the baseline. If reactive hypoglycemia is suspected, a 4-hour oral glucose tolerance test with serial insulin measurements can confirm the pattern. Dietary intervention (protein-pairing, reducing refined carbohydrate load, spacing meals at 3 to 4 hour intervals) resolves reactive hypoglycemia symptoms in most patients within 2 weeks.

Perimenopause and Menopause: The 40-to-55 Window

The menopausal transition is one of the highest-risk windows for new-onset mood disturbance in women who had no prior psychiatric history. The Study of Women's Health Across the Nation (SWAN), a longitudinal cohort of 3,302 women, found that women in the late perimenopausal stage were 2.5 times more likely to report depressive symptoms than premenopausal women 10.

Perimenopause typically spans 4 to 8 years. During this window, estradiol levels fluctuate erratically rather than declining linearly. A single month might see estradiol spike to 400 pg/mL and then crash to 20 pg/mL. These wide oscillations produce vasomotor symptoms (hot flashes), sleep disruption, and direct serotonergic destabilization, all of which converge on mood.

The 2022 position statement from The Menopause Society (formerly NAMS) concluded that "hormone therapy is the most effective treatment for vasomotor symptoms and has been shown to improve mood in symptomatic perimenopausal women" 11. Transdermal estradiol (0.025 to 0.05 mg/day) combined with micronized progesterone (100 to 200 mg nightly) addresses both vasomotor and mood symptoms with favorable safety profiles in women under 60 or within 10 years of menopause onset.

Not every perimenopausal woman needs HRT for mood. If vasomotor symptoms are absent and mood is the primary complaint, SSRIs (particularly escitalopram 10 to 20 mg or sertraline 50 to 100 mg) are effective alternatives and are FDA-approved for this use case through their depression/anxiety indications.

PMDD: When Mood Swings Follow the Menstrual Cycle

Premenstrual dysphoric disorder affects 3% to 8% of reproductive-age women, per DSM-5-TR criteria 12. PMDD is categorically different from PMS. The hallmark is severe mood reactivity, irritability, or depressive episodes confined to the luteal phase (the 10 to 14 days before menstruation) that resolve within a few days of bleeding onset.

The pathophysiology is not low progesterone or low estrogen per se. Rather, PMDD reflects abnormal central sensitivity to normal hormonal fluctuations. Allopregnanolone, a progesterone metabolite, modulates GABA-A receptors. Women with PMDD have an altered neuroactive steroid response to this modulation 13.

Diagnosis requires prospective daily symptom tracking for at least two consecutive cycles. Retrospective recall is unreliable. The DRSP (Daily Record of Severity of Problems) is the validated instrument.

Treatment is well-established. SSRIs given only during the luteal phase (sertraline 50 mg or fluoxetine 20 mg from ovulation through day 2 of menses) produce response rates of 60% to 70%, comparable to continuous dosing 14. For women who do not respond to SSRIs, GnRH agonists (leuprolide) with add-back HRT are second-line but carry bone density considerations with long-term use.

Low Testosterone in Men: Beyond Libido

The conversation about low testosterone tends to center on sexual function and muscle mass. Mood is equally affected. The European Male Ageing Study (EMAS, N=3,369) found that men with total testosterone below 317 ng/dL had significantly higher scores on depression and anxiety scales, independent of age, BMI, and comorbidities 15.

Testosterone influences mood through multiple pathways: direct effects on amygdala reactivity, modulation of cortisol via the HPA axis, and aromatization to estradiol in the brain (which in turn affects serotonin). The clinical picture in testosterone-deficient men is not classic depression. Instead, patients describe episodic irritability, reduced stress tolerance, emotional flatness punctuated by anger, and loss of motivation.

The Endocrine Society recommends confirming low testosterone with two morning serum total testosterone measurements below 300 ng/dL before initiating therapy 3. If confirmed, testosterone replacement (topical gel, intramuscular injection, or subcutaneous pellet) typically produces mood improvement within 3 to 6 weeks, with full stabilization by 3 months.

Dr. Shalender Bhasin, principal investigator of the TTrials, has stated: "The mood benefits of testosterone therapy are most pronounced in men with the lowest baseline testosterone levels and the most significant mood symptoms at entry" 4.

Medications and Substances That Trigger Mood Swings

Several medication classes cause mood instability as a direct pharmacologic effect, not a rare side effect.

Corticosteroids are among the worst offenders. A systematic review in Annals of Internal Medicine found that psychiatric symptoms (including mania, depression, and mixed states) occurred in 5% to 18% of patients receiving prednisone at doses above 20 mg/day 16. Symptoms can appear within days of starting therapy and may persist for weeks after discontinuation.

Hormonal contraceptives affect a subset of women. A Danish population study (N=1,061,997) showed that current users of combined oral contraceptives had a 1.23 relative risk of first depression diagnosis and a 1.34 relative risk among adolescents aged 15 to 19 17. The levonorgestrel IUD and depot medroxyprogesterone acetate (Depo-Provera) showed the highest relative risk among progestin-only methods.

Other agents to consider: isotretinoin (Accutane) has FDA black-box warnings related to psychiatric effects, though causality remains debated. Interferons used for hepatitis C and multiple sclerosis carry well-documented depression and irritability risk. Benzodiazepine withdrawal produces rebound anxiety and emotional dysregulation, sometimes lasting weeks.

Alcohol is the most common substance trigger. Even moderate intake (2 to 3 drinks daily) disrupts GABAergic and glutamatergic balance, fragments sleep architecture, and produces next-day irritability. Cannabis, particularly high-THC strains, can trigger mood lability in susceptible individuals.

A complete medication and substance review should be part of every mood swing evaluation.

Psychiatric Conditions: Bipolar Disorder and Beyond

Not all mood swings are hormonal or metabolic. Bipolar II disorder is the most commonly missed psychiatric cause because its hypomanic episodes are subtle and often ego-syntonic (they feel productive and energizing).

The World Health Organization's World Mental Health Survey found that bipolar disorder affects approximately 2.4% of the global population, yet the average delay from symptom onset to correct diagnosis is 6 to 8 years 18. During that delay, 40% of bipolar II patients receive a unipolar depression diagnosis and are treated with antidepressants alone, which can worsen cycling.

Key distinguishing features of bipolar mood swings versus hormonal mood swings: bipolar episodes last days to weeks (not hours), involve changes in sleep need (not insomnia, but reduced need), and include grandiosity or pressured speech during highs. The Mood Disorder Questionnaire (MDQ) is a validated 13-item screening tool with 73% sensitivity and 90% specificity for bipolar spectrum disorders 19.

Borderline personality disorder (BPD) produces mood swings that are rapid (minutes to hours), interpersonally triggered, and accompanied by fear of abandonment and identity disturbance. The time course and triggers differ from hormonal causes.

When psychiatric and hormonal causes overlap, both need treatment. Starting an SSRI for depression in a woman with undiagnosed hypothyroidism produces partial response at best. Treating thyroid disease in a patient with concurrent bipolar disorder stabilizes one axis but not the other.

The Diagnostic Workup: What Labs to Order

A systematic approach prevents missed diagnoses. The following panel covers the majority of treatable causes.

Tier 1 (order for all patients with unexplained mood swings):

• TSH and free T4
• Fasting glucose and HbA1c
• Complete blood count (to screen for anemia)
• Comprehensive metabolic panel (electrolytes, calcium, liver function)
• Total testosterone (morning draw, both sexes)

Tier 2 (order based on clinical suspicion):

• Free T3 and thyroid antibodies (if TSH is borderline)
• Estradiol and progesterone (day 3 and day 21 of cycle in premenopausal women)
• FSH (if perimenopause suspected)
• DHEA-S and cortisol (if adrenal dysfunction suspected)
• Fasting insulin (if insulin resistance suspected)
• Vitamin D, B12, folate (deficiencies contribute to mood symptoms)
• Prolactin (if amenorrhea or galactorrhea present)

Tier 3 (psychiatric screening):

• PHQ-9 for depression
• GAD-7 for anxiety
• MDQ for bipolar screening
• DRSP daily tracking for PMDD (2 cycles minimum)

The sequence matters. Correct any hormonal or metabolic abnormality first, reassess mood at 6 to 8 weeks, and only then consider psychiatric diagnosis if symptoms persist. Prescribing an antidepressant before checking a TSH is a common and avoidable clinical error.

Treatment: Matching Intervention to Cause

Treatment depends entirely on etiology. There is no single "mood swing medication."

For hypothyroidism-driven mood swings, levothyroxine titrated to TSH 1.0 to 2.0 mIU/L resolves symptoms in most patients within 8 weeks 5. For perimenopausal mood symptoms, transdermal estradiol plus micronized progesterone is first-line per The Menopause Society 11. For male hypogonadism, testosterone replacement per Endocrine Society protocols 3. For PMDD, luteal-phase SSRIs 14. For reactive hypoglycemia, dietary restructuring (protein at every meal, limiting refined carbohydrates to <30g per sitting). For bipolar disorder, mood stabilizers (lithium, valproate, or lamotrigine) remain the standard of care, not antidepressants alone.

Adjunctive interventions apply across causes. Sleep optimization (7 to 9 hours, consistent sleep-wake times) reduced emotional reactivity by 60% in an fMRI study of amygdala response to negative stimuli 20. Regular aerobic exercise (150 minutes per week at moderate intensity) has effect sizes comparable to SSRIs for mild-to-moderate depression, per a 2023 Cochrane review 21. Cognitive behavioral therapy (CBT) addresses maladaptive thought patterns that amplify physiologic mood shifts.

Patients with identified hormonal causes who also meet criteria for a psychiatric diagnosis need both treated simultaneously. Starting HRT for perimenopause while initiating an SSRI for concurrent major depression produces better outcomes than either alone, per SWAN follow-up data 10.