Hypothyroidism vs. Hyperthyroidism: Symptoms, Causes & Treatment

The thyroid—a butterfly-shaped gland in your neck—orchestrates metabolism through thyroxine (T4) and triiodothyronine (T3). When it under- or over-produces, every system feels the ripple.

Hypothyroidism (Underactive Thyroid)

More common in women; typical onset adulthood (30–60), but can occur at any age.

Common Symptoms

• Fatigue, sluggishness, "brain fog"
• Weight gain despite unchanged diet
• Cold intolerance
• Constipation
• Dry skin, brittle hair, hair loss
• Muscle weakness, cramps, joint stiffness
• Depression, memory issues, slowed thinking
• Heavy/irregular periods, fertility challenges
• Elevated cholesterol, slow heart rate
• Goiter (neck swelling)

Common Causes

• Hashimoto's thyroiditis (autoimmune) — #1 cause in iodine-sufficient areas
• Iodine deficiency (global #1 cause)
• Thyroid surgery, radioactive iodine treatment
• Medications (lithium, amiodarone, checkpoint inhibitors)
• Pituitary/hypothalamic dysfunction (secondary)

Treatment

Levothyroxine (T4) daily — lifelong, dose titrated to normalize TSH. Take on empty stomach, 30–60 min before food/coffee/other meds. Monitor TSH every 6–12 weeks until stable, then 6–12 months.

Hyperthyroidism (Overactive Thyroid)

Also more common in women; often presents 20s–40s.

Common Symptoms

• Unintentional weight loss despite increased appetite
• Heat intolerance, excessive sweating
• Palpitations, tachycardia, atrial fibrillation
• Anxiety, irritability, insomnia, tremors
• Diarrhea, frequent bowel movements
• Muscle weakness (proximal), fatigue
• Exophthalmos (bulging eyes) — specific to Graves' disease
• Goiter, warm moist skin, hair thinning
• Menstrual irregularities, infertility

Common Causes

• Graves' disease (autoimmune, TSH receptor antibodies) — #1 cause
• Toxic multinodular goiter / toxic adenoma
• Thyroiditis (subacute, postpartum, drug-induced) — transient thyrotoxicosis
• Excess iodine (amiodarone, contrast, supplements)
• TSH-secreting pituitary adenoma (rare)

Treatment

• Antithyroid drugs (ATDs): Methimazole (preferred), PTU (1st trimester pregnancy). 12–18 month course; remission ~30–50%.
• Radioactive iodine (RAI) ablation: Definitive, outpatient. Leads to hypothyroidism → lifelong levothyroxine. Not in pregnancy.
• Thyroidectomy: Surgery for large goiters, suspicion of cancer, pregnancy if ATDs fail, patient preference. Requires experienced surgeon.
• Beta-blockers (propranolol) for symptomatic control while definitive treatment takes effect.

Monitoring Is Lifelong

Both conditions require regular TSH, free T4, free T3 monitoring. Dose adjustments happen with life changes (pregnancy, aging, weight change, new meds). With proper management, thyroid patients live full, healthy lives.