Synthroid and CBD — interaction profile and FAQ
Cannabidiol (CBD) is widely used as an over-the-counter wellness product, and many people taking Synthroid (Levothyroxine) — used for Synthroid is approved for hypothyroidism of any cause (Hashimoto thyroiditis, post-thyroidectomy, post-radioiodine, congenital), goitre and TSH suppression after differentiated thyroid cancer. — wonder whether the two are safe to combine. Unlike most herbal products, CBD has documented interactions with several drug-metabolising enzymes, which means it can change blood levels of co-administered medications. Below is a focused look at the Synthroid-and-CBD question at the 25mcg, 50mcg, 75mcg, 100mcg, 150mcg dosing strengths.
How CBD can affect Synthroid blood levels
CBD inhibits several cytochrome P450 enzymes — most notably CYP3A4, CYP2C19 and CYP2D6 — which together metabolise a large fraction of prescription medications. Synthroid, with active ingredient Levothyroxine, may or may not be metabolised by these enzymes; if it is, concomitant CBD can raise Synthroid blood levels and increase the risk of dose-related side effects. Conversely, in some pathways, induction or competition for transporters can lower exposure. The clinically relevant size of this effect depends on the CBD dose, formulation and individual hepatic metabolism.
Practical guidance for combined use
According to general clinical guidance, anyone planning to combine Synthroid at the 25mcg, 50mcg, 75mcg, 100mcg, 150mcg doses with regular CBD use should discuss this with the prescriber and ideally check the Synthroid prescribing information and an interaction database (e.g. Lexicomp, the FDA Drug Interactions guidance) for the Levothyroxine entry. Practical steps include starting at low CBD doses, separating CBD and Synthroid doses by several hours where feasible and monitoring for side effects (sedation, dizziness, gastrointestinal symptoms or laboratory changes) during the first weeks. Pure isolate CBD has fewer co-formulants but the CYP-inhibition signal is similar.
Frequently asked questions
Is it safe to use CBD with Synthroid? ▾
Whether CBD is safe to combine with Synthroid depends on the metabolic pathway of Levothyroxine, the CBD dose and the indication for which Synthroid is taken at the 25mcg, 50mcg, 75mcg, 100mcg, 150mcg dose. For many medications the interaction is mild and manageable; for narrow-therapeutic-index drugs (anticoagulants, anti-epileptics, immunosuppressants and some psychiatric medications) the combination warrants closer follow-up. Discuss with the prescriber and check an interaction database before starting CBD.
How much time should I leave between CBD and Synthroid? ▾
For most medications, separating CBD and Synthroid by several hours reduces, though does not eliminate, the metabolic interaction; for steady-state regimens with cumulative drug levels, simple time separation has limited effect. According to general pharmacological principles, the more meaningful step is establishing a stable CBD dose, monitoring symptoms and laboratory values, and adjusting Synthroid dosing under the prescriber's guidance rather than relying on timing alone.
More on Synthroid
- With alcoholSynthroid and alcohol — is it safe to drink?
- With foodShould Synthroid be taken with food?
- Side effectsSynthroid side effects: common, rare and warning signs
- Dosage guideSynthroid dosage guide: how much to take and when
- OnsetHow fast does Synthroid start working?
- DurationHow long does Synthroid last?
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.