Updated: January 23, 2026
Unithroid Side Effects: What to Expect and When to Call Your Doctor
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Peter Daggett
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Overview
Most Unithroid side effects are signs of overtreatment — not the drug itself. Learn which side effects are common, which are serious, and when to call your doctor.
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Based on 57 real pharmacy checks · 1 patients helped
Verified 3h ago
Understanding Unithroid side effects is important — but it helps to understand why they occur. Most side effects associated with Unithroid (levothyroxine sodium) are not caused by the drug itself in the traditional sense. They are symptoms of too much thyroid hormone in your body (hyperthyroidism or overtreatment), which can happen when your dose is too high. When your dose is correct and your TSH is in the normal range, most patients tolerate levothyroxine very well.
Common Side Effects of Unithroid
The following side effects are most frequently reported with Unithroid, especially during the early weeks of treatment or after a dose increase:
Temporary hair loss: Thinning hair is common in the first 3-6 months of starting levothyroxine. This typically resolves on its own as your thyroid levels stabilize.
Headache:
Insomnia and sleep disturbances:
Nervousness and irritability:
Fever, hot flashes, and sweating:
Heart palpitations:
Changes in menstrual cycle:
Appetite changes and weight loss:
Diarrhea:
Heat intolerance:
If you experience these side effects, notify your doctor. Your dose may be too high and a reduction may be needed. Do not reduce your dose on your own — levothyroxine dose changes require TSH monitoring to guide adjustments.
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Serious Side Effects: Call Your Doctor Right Away
These side effects are potentially serious and require prompt medical attention:
Chest pain, rapid or irregular heartbeat (arrhythmia): Overtreatment can precipitate arrhythmias or worsen existing heart disease — especially in elderly patients. Call your doctor immediately or seek emergency care.
Sudden bone or joint pain: Long-term overtreatment increases bone resorption and can reduce bone mineral density — particularly in postmenopausal women. Sudden hip, wrist, or back pain may signal a stress fracture.
Signs of allergic reaction: Hives, difficulty breathing, swelling of face, lips, tongue, or throat. Seek emergency help immediately. Note: true allergy to levothyroxine itself is rare; reactions are more commonly due to inactive ingredients (Unithroid contains lactose and dyes).
Seizures, stroke, or loss of consciousness (overdose): Levothyroxine overdose is a medical emergency. Symptoms include severe tremor, extreme agitation, chest pain, stroke, coma. Call 911 immediately.
Boxed Warning: Do Not Use for Weight Loss
Unithroid carries a boxed warning (the FDA's most serious warning level) stating that thyroid hormones should not be used for weight loss or obesity treatment. In patients with normal thyroid function (euthyroid), doses within the daily hormonal range will not cause weight loss. Larger doses may produce serious or life-threatening effects, particularly when combined with appetite suppressants or sympathomimetic amines.
Side Effects of Undertreatment (Too Low a Dose)
Undertreatment — taking too low a dose or missing doses — can also cause symptoms. These are hypothyroid symptoms that persist or return despite being on Unithroid:
Fatigue and low energy
Unexplained weight gain
Cold intolerance
Brain fog and memory problems
Constipation
Depression or low mood
Dry skin and hair
If you are experiencing these symptoms while on Unithroid, contact your doctor to get your TSH checked. Your dose may need to be increased, or you may have an absorption problem (e.g., calcium or iron supplements taken too close to your Unithroid dose).
Side Effects in Special Populations
Elderly patients: More susceptible to cardiac side effects; start at lower doses (25 mcg/day) and titrate slowly.
Pregnant patients: Higher doses are often needed. Undetected undertreatment risks fetal neurodevelopment; TSH must be monitored every 4 weeks in the first half of pregnancy.
Patients with cardiovascular disease: Risk of arrhythmia and angina with overtreatment; start at reduced doses and monitor cardiac symptoms closely.
Side effects can also be caused or worsened by drug interactions. See our guide on Unithroid drug interactions to learn what to avoid.
Real-time availability
Is Unithroid in stock near you?
Verified 3h ago
Based on 57 real pharmacy checks · 1 patients helped
Unithroid is in a shortage right now — Medfinder calls pharmacies near you to track down the ones that have it.
As of August 25, 2026, 2:00 PM ET, Unithroid is currently experiencing a shortage. Across 57 pharmacy checks Medfinder placed in the last 30 days, Unithroid was confirmed in stock 0% of the time.
- Pharmacy checks
- 57
- FDA status
- Not listed
- Updated
- 3h ago
Unithroid is not on the FDA's active shortage list. Medfinder's own pharmacy calls put real-time availability at 0% across 57 checks in the last 30 days. Availability varies by metro, with the most pharmacy activity recorded around Coral Springs, FL. These numbers are recomputed continuously from live pharmacy calls, so this page reflects current conditions rather than a static estimate.
Unithroid availability questions
Is Unithroid in stock right now?
As of August 25, 2026, 2:00 PM ET, Unithroid was confirmed in stock at 0% of 57 pharmacies Medfinder checked in the last 30 days. Availability changes daily, so we re-check in real time when you search.
How does Medfinder help me find Unithroid?
Medfinder calls pharmacies in your area to verify whether Unithroid and your specific dose are in stock, then sends you the pharmacy name, address, and phone number.
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Sources: FDA Drug Shortages + Medfinder pharmacy data · Methodology · Full Unithroid data
Frequently Asked Questions
Temporary hair loss is a common side effect in the first 3-6 months of starting levothyroxine or changing your dose. This is typically due to the transition in thyroid hormone levels, not the drug itself, and usually resolves as your levels stabilize. If hair loss continues beyond 6 months, contact your doctor to check your TSH.
Yes. Heart palpitations can occur with Unithroid, typically as a sign that your dose is too high. If you experience palpitations, rapid heartbeat, or chest pain, contact your doctor promptly. Do not stop taking Unithroid on your own — your doctor will check your TSH and adjust your dose appropriately.
Unithroid itself typically does not cause weight gain. Weight gain while on Unithroid usually indicates undertreatment (dose too low) or hypothyroidism returning. If you are gaining weight unexpectedly, get your TSH checked — your dose may need to be increased.
If you accidentally take an extra dose of Unithroid, contact your doctor or Poison Control (1-800-222-1222). Symptoms of overdose include severe tremor, extreme agitation, rapid heartbeat, chest pain, shortness of breath, or stroke. If symptoms are severe, call 911 immediately.
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