Symptoms from Stopping Synthroid for Two Weeks
If you discontinue Synthroid (levothyroxine) for two weeks, you will likely develop symptoms of hypothyroidism including fatigue, weight gain, cold intolerance, constipation, dry skin, muscle weakness, and cognitive slowing—though the severity depends on whether you have any residual thyroid function.
Timeline of Symptom Development
The onset and severity of symptoms after stopping levothyroxine depends on the drug's long half-life and your underlying thyroid function:
Week 1 (Days 1-7): Most patients remain relatively asymptomatic due to levothyroxine's long half-life. TSH begins rising but free T4 levels remain near normal 1.
Week 2 (Days 8-14): This is when symptoms typically emerge. By day 14, approximately 71% of patients have TSH levels ≥30 mIU/L, and most have free T4 levels below normal range 1. Clinical symptoms of hypothyroidism become apparent during this period.
Expected Symptoms
Based on FDA labeling, inadequate levothyroxine dosage (or complete discontinuation) will produce the classic signs and symptoms of hypothyroidism 2:
General symptoms:
- Fatigue and lethargy
- Weight gain
- Cold intolerance
- Decreased appetite
Neurological/Cognitive:
- Mental slowing and impaired concentration
- Depression and emotional changes
- Headache
Musculoskeletal:
- Muscle weakness
- Joint aches
Cardiovascular:
- Bradycardia (slow heart rate)
- Potential worsening of heart failure if pre-existing
Gastrointestinal:
- Constipation
Dermatologic:
- Dry skin
- Hair loss
Other:
- Menstrual irregularities in women
Critical Considerations
Cardiovascular risk: If you have underlying coronary heart disease, abrupt discontinuation poses significant risk. The guidelines emphasize that patients with known coronary disease require careful monitoring, as hypothyroidism can precipitate angina 3.
Adrenal insufficiency: In rare cases, patients with undiagnosed adrenal insufficiency can experience life-threatening exacerbation when thyroid hormone is withdrawn 3. This is uncommon but serious.
Age-related factors: Older patients may experience more pronounced cardiovascular symptoms and are at higher risk for atrial fibrillation with thyroid hormone fluctuations 3, 2.
Why This Matters
The severity of symptoms correlates with:
- Your underlying thyroid function: If you have complete thyroid failure (post-thyroidectomy or radioablation), symptoms will be more severe than if you have partial thyroid function
- Your baseline dose: Higher doses suggest more severe hypothyroidism and predict worse symptoms upon discontinuation
- Duration off medication: Symptoms progressively worsen beyond two weeks
What Happens Physiologically
When levothyroxine is stopped, TSH rises rapidly as the pituitary attempts to stimulate the thyroid. By 14 days, TSH elevation is substantial and free T4 drops below normal in most patients 1. This hormonal shift directly causes the clinical symptoms listed above.
Common Pitfalls
Do not stop levothyroxine abruptly without medical supervision, especially if you:
- Have heart disease
- Are elderly
- Take high doses (>100 µg/day)
- Have had your thyroid removed or ablated
Missed doses should be made up when recognized, even if taking multiple doses on subsequent days 3. The guideline explicitly states this is preferable to prolonged gaps in therapy.
If you've already stopped for two weeks and are symptomatic, restarting levothyroxine will gradually reverse symptoms over several weeks as thyroid hormone levels normalize. TSH normalization typically requires 4-8 weeks after restarting therapy 3.