Levothyroxine and Ritonavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ritonavir
Levothyroxine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Loss of levothyroxine efficacy
Interaction Deep Dive
An HIV-positive woman with prior thyroidectomy was observed to have signs and symptoms of hypothyroidism despite levothyroxine dose increases while taking an antiretroviral regimen including ritonavir. The levothyroxine dosage was continually increased, and symptoms of fatigue, anorexia, and anemia were present, while TSH and free T4 levels remained elevated. After antiretroviral therapy was changed to a regimen without ritonavir, her TSH normalized and remained normal for 18 months thereafter while on a stable dosage of levothyroxine2. A patient stabilized on levothyroxine experienced loss of efficacy when ritonavir was added to his therapeutic regimen, necessitating a doubling of the levothyroxine dose. Following the discontinuation of ritonavir, levothyroxine was decreased to the previous daily dose and the patient remained asymptomatic. Levothyroxine undergoes conjugation with glucuronic and sulfuric acids, and ritonavir may have induced glucuronyl transferases 3. In another case report, an HIV-positive female on lopinavir/ritonavir experienced persistent hypothyroidism, despite increasing doses of levothyroxine. The hypothyroidism resolved upon discontinuation of lopinavir/ritonavir and recurred upon rechallenge 1.
Why it happens (mechanism)
Induction of glucuronyl transferases by ritonavir
Literature reports
3 reports — tap to read
a) A 37-year-old HIV-positive woman with prior thyroidectomy due to multinodular goiter was observed to have signs and symptoms of hypothyroidism despite levothyroxine dose increases while taking an antiretroviral regimen including ritonavir. As her viral load was undetectable on abacavir 600 mg/lamivudine 300 mg once daily and lopinavir 200 mg/ritonavir 50 mg twice daily (initiated due to pregnancy at the time), this regimen was continued after her thyroidectomy and through 2 additional pregnancies. Post-thyroidectomy, her TSH increased from 1.32 to 94.3 milli-international units/L (reference range: 0.3 to 0.6 milli-international units/L), and free T4 decreased from 0.89 to 0.47 nanograms/dL (11.5 to 6.1 picomol/L; reference range: 0.7 to 1.9 nanogram/dL (9 to 23 picomol/L)). After her final pregnancy, the presumed interaction between ritonavir and levothyroxine was managed by increasing the levothyroxine dosage, starting with 75 mcg/day and increasing to 175 mcg/day. She had symptoms of fatigue, anorexia, and anemia while TSH and free T4 levels remained elevated. After antiretroviral therapy was changed to abacavir 600 mg/lamivudine 300 mg once daily with dolutegravir 50 mg daily instead of ritonavir-boosted therapy, her TSH decreased to 0.12 milli-international units/L, and remained normal for 18 months thereafter, while taking levothyroxine 125 mcg/day 2.
b) An HIV-positive female on lopinavir/ritonavir experienced persistent hypothyroidism, despite increasing doses of levothyroxine. Approximately 2 years after starting lopinavir/ritonavir, zidovudine, and lamivudine, she required a total thyroidectomy followed by radioiodine therapy for thyroid papillary carcinoma. Levothyroxine was started. Despite increases in levothyroxine dose to 225 mcg/day and addition of liothyronine, the TSH remained elevated at 47.5 mU/L; T4 remained low at 8.5 pmol/L (T3, 3.2 pmol/L); and the patient was symptomatic. Normal values were 0.2 to 5.1 mU/L for TSH, 11 to 24 pmol/L for serum free T4, and 2.5 to 7 pmol/L for serum free T3. Within 2 months after discontinuation of lopinavir/ritonavir, TSH, T4, and T3 normalized . A rechallenge with lopinavir/ritonavir 9 months later resulted in elevated TSH (18.1 mU/L to 42.9 mU/L) and reduced T4 (8.5 pmol/L to 10.6 pmol/L). Within 3 months of discontinuation of lopinavir/ritonavir and initiation of 3 nucleoside reverse transcriptase inhibitors, the TSH and T4 normalized 1.
c) An HIV-positive male receiving long-term therapy with interferon-alfa was diagnosed with autoimmune thyroiditis secondary to interferon use when his thyroid stimulating hormone (TSH) level increased to 9.25 mU/L. He responded to levothyroxine 0.125 mg daily and his thyroid indices returned to normal levels. One year later, ritonavir was added to his antiretroviral regimen because of increasing viral load. One month after initiating ritonavir 600 mg twice daily, his TSH level was 18.47 mU/L and the patient was extremely lethargic. Increasing his levothyroxine dose to 0.25 mg daily reduced his TSH to 7.35 mU/L. Because of hepatotoxicity, indinavir was substituted for ritonavir and levothyroxine was reduced to 0.125 mg daily to avoid toxicity. He remained asymptomatic on this levothyroxine dose and his TSH stabilized at 7.32 mU/L 3.
Common questions
Can I take Levothyroxine and Ritonavir together?
Loss of levothyroxine efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levothyroxine and Ritonavir interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Levothyroxine or Ritonavir need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (3)
- Touzot M, Beller CL, Touzot F, et al: Dramatic interaction between levothyroxine and lopinavir/ritonavir in a HIV-infected patient. AIDS 2006; 20(8):1210-1212. PubMed
- Sahajpal R, Ahmed RA, Hughes CA, et al: Probable interaction between levothyroxine and ritonavir: case report and literature review. Am J Health Syst Pharm 2017; 74(8):587-592. PubMed
- Tseng A & Fletcher D: Interaction between ritonavir and levothyroxine. AIDS 1998; 12:2235-2236.
Keep reading about Ritonavir
Keep reading about Levothyroxine
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