Levothyroxine

For an informed discussion with your doctor or pharmacist. This information collection is not a clinically validated interaction checker. Missing data do not establish safety. Do not change or stop prescribed medicines on the basis of this information. The findings apply to the specific conditions studied; laboratory and animal studies cannot be directly extrapolated to humans.

Active substance: Levothyroxine

Examples of brand names: Euthyrox [DE]

ATC code: H03AA01

Main use (for orientation): Hypothyroidism

Documented research summary

Small paediatric observations in 2021/2023: concomitant levothyroxine associated with greater CBD exposure. In 2023 n=22, including 7 receiving levothyroxine; adjusted CBD trough concentration +109.6% (95% CI 49.2–194.5). A 2025 older-adult cannabis cohort reports more heart-failure events with levothyroxine plus cannabis, but no significant association with thyrotoxicosis/acute coronary syndrome/stroke. No causal CYP evidence or equivalence with pure CBD.

Uncertainties and limitations

Small paediatric cohort receiving multiple therapies; observational association, not causality. Dataset may overlap with the 2021 paper from the same centre.

Older-adult study without cannabinoid type/dose/route, residual confounding; no verified heart-failure effect estimate adopted without Appendix 6.

Relevant methods/results/limitations of PMC10459683/12704418 read.

Separately recorded findings

2 separately recorded findings. Each statement applies to its documented study context.

CBD – clinical signals

Finding ID: B0395

Type of result: Observed association, not confirmation of causality

Observation: 2023: adjusted CBD trough concentration 109.6% higher with concomitant levothyroxine (95% CI 49.2–194.5). Earlier pharmacokinetic paper, n=12, also reports a signal.

Mechanism: Co-medication associated with higher CBD trough concentration; mechanism not causally demonstrated

Study type: Paediatric observational studies; not a randomised interaction assessment

Context studied: 2023: n=22 children with difficult-to-treat epilepsies, 7 receiving levothyroxine; multiple medicines. Median CBD 8.8 mg/kg/day according to the abstract.

Clinical interpretation: Interpret within the stated study context; no independent dosage or treatment recommendation.

Limitations and uncertainties: No randomised allocation, small sample, food/ketogenic diet/polytherapy as influencing factors. Do not extrapolate the T4 effect to liothyronine; possible cohort overlap.

Original sources for this finding: Real-World Evidence of Factors Affecting Cannabidiol Exposure in Children with Drug-Resistant Developmental and Epileptic Encephalopathies. [RMED37631333]; Pharmacokinetics of cannabidiol in children with refractory epileptic encephalopathy. [RMED33280111]

Medical cannabis; composition unknown – clinical signals

Finding ID: B0396

Type of result: Association with positive and non-significant endpoints

Observation: Among 2,499 people exposed to cannabis plus levothyroxine, emergency visits/hospitalisation for heart failure were more likely; no significant association for thyrotoxicosis, acute coronary syndrome or stroke.

Mechanism: Co-medication association; pharmacokinetic/pharmacodynamic mechanism not established

Study type: Retrospective population-based cohort in older adults

Context studied: Overall cohort: 12,599 people prescribed cannabis, 48,651 controls; aged ≥66 years.

Clinical interpretation: Interpret within the stated study context; no independent dosage or treatment recommendation.

Limitations and uncertainties: Cannabinoid type, dose and route absent; residual confounding. Not a causal pure-CBD interaction. Heart-failure effect estimate from unassessed Appendix 6 not adopted.

Original sources for this finding: Concomitant use of medical cannabis and drugs associated with risks of interaction in older patients: a longitudinal cohort study. [RMED41396801]

References and access status

[RLABEL_D0262] Levothyroxin – DailyMed Produktkennzeichnung

Original source / bibliographic reference

Authors: Regulatory product information; respective marketing authorisation holder

Year: 2026

Source type: Product information / SmPC / US Prescribing Information

Source access – 23 October 2026: Source destination was accessible when checked.

Bibliographic attribution or source identity cross-checked.

[RMED37631333] Real-World Evidence of Factors Affecting Cannabidiol Exposure in Children with Drug-Resistant Developmental and Epileptic Encephalopathies.

Original source / bibliographic reference

Authors: Brstilo L, Reyes Valenzuela G, Caraballo R, Pérez Montilla C, García Bournissen F, Cáceres Guido P, Schaiquevich P.

Year: 2023

Source type: Original publication; see finding for study type

DOI: 10.3390/pharmaceutics15082120

PMID: 37631333

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

PubMed Central – full-text access according to the literature database – Archive attribution confirmed by Europe PMC metadata. Direct retrieval was not fully verified here; access may require a browser check.

Europe PMC – full-text access according to the literature database – Listed as freely available HTML full text in the official Europe PMC metadata. Direct retrieval was not fully verified here.

[RMED33280111] Pharmacokinetics of cannabidiol in children with refractory epileptic encephalopathy.

Original source / bibliographic reference

Authors: Cáceres Guido P, Riva N, Caraballo R, Reyes G, Huaman M, Gutierrez R, Agostini S, Fabiana Delaven S, Pérez Montilla CA, García Bournissen F, Schaiquevich P.

Year: 2021

Source type: Original publication; see finding for study type

DOI: 10.1111/epi.16781

PMID: 33280111

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

[RMED41396801] Concomitant use of medical cannabis and drugs associated with risks of interaction in older patients: a longitudinal cohort study.

Original source / bibliographic reference

Authors: Bérété ZC, Sebgo AA, Eurich DT, Dubois C, Dyck JR, Hanlon JG, Zongo A.

Year: 2025

Source type: Original publication; see finding for study type

DOI: 10.1093/ageing/afaf359

PMID: 41396801

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

PubMed Central – full-text access according to the literature database – Archive attribution confirmed by Europe PMC metadata. Direct retrieval was not fully verified here; access may require a browser check.

Europe PMC – full-text access according to the literature database – Listed as freely available HTML full text in the official Europe PMC metadata. Direct retrieval was not fully verified here.

Research as of 23 October 2026. Not all original full texts could be reviewed in full. Source accessibility and the strength of scientific evidence must be assessed separately. An accessible link does not establish medical approval; a bibliographic record with an abstract does not replace the original full text.

Drug search and explanation of the evidence · Guide: cannabinoids and medicines · Author and responsibility