Can I Take St. John's Wort with Farxiga (Dapagliflozin)?

What Is Farxiga and Why Does Its Blood Level Matter?

Dapagliflozin (Farxiga, AstraZeneca) is a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor approved by the FDA for type 2 diabetes, heart failure with reduced ejection fraction (HFrEF), and chronic kidney disease (CKD) [1]. It works by blocking glucose reabsorption in the proximal tubule of the kidney, causing urinary glucose excretion of roughly 70 grams per day at the 10 mg dose [2].

Its benefits are dose-exposure dependent. The DAPA-HF trial (N=4,744) showed that dapagliflozin 10 mg reduced the composite of worsening heart failure or cardiovascular death by 26% versus placebo (hazard ratio 0.74, 95% CI 0.65 to 0.85, P<0.001) [3]. The DAPA-CKD trial (N=4,304) showed a 39% reduction in kidney function decline or death from kidney or cardiovascular causes (HR 0.61, 95% CI 0.51 to 0.72, P<0.001) [4]. Those numbers depend on adequate drug exposure. Anything that meaningfully lowers dapagliflozin plasma concentrations erodes those benefits.

How Dapagliflozin Is Metabolized

The primary metabolic pathway for dapagliflozin is glucuronidation via UGT1A9 in the liver and kidney, producing the inactive metabolite dapagliflozin 3-O-glucuronide [5]. CYP3A4 plays a secondary but measurable role, particularly for minor oxidative pathways [5]. P-glycoprotein (P-gp) influences intestinal absorption and renal tubular secretion of the parent compound [6].

The FDA-approved prescribing information for Farxiga explicitly states that co-administration with inducers of UGT1A9 or CYP3A4 may decrease dapagliflozin exposure, and it names rifampin as the prototypical inducer example, noting that rifampin co-administration reduced dapagliflozin AUC by approximately 22% [1].

Why Plasma Exposure Matters Clinically

A 20 to 25% reduction in AUC does not simply subtract 20 to 25% from the drug's effect in a linear way. SGLT2 inhibition is not fully saturated at the standard 10 mg dose. Animal and human pharmacodynamic data indicate that below certain plasma thresholds, urinary glucose excretion falls sharply because renal glucose transport capacity rebounds [2]. Patients taking 5 mg dapagliflozin, already a submaximal dose, face proportionally greater risk of losing glycemic efficacy.

What Is St. John's Wort and How Does It Affect Drug Metabolism?

St. John's Wort (Hypericum perforatum) is one of the most widely used herbal supplements in the United States, with surveys suggesting roughly 3 to 5% of adults with depression have tried it [7]. It is sold over the counter in doses commonly ranging from 300 mg to 1,800 mg per day, usually standardized to 0.3% hypericin or 3 to 5% hyperforin content.

The CYP3A4 and P-gp Induction Mechanism

The pharmacologically active constituent responsible for drug interactions is hyperforin, not hypericin. Hyperforin activates the pregnane X receptor (PXR), a nuclear transcription factor that upregulates expression of CYP3A4, CYP2C9, P-glycoprotein (MDR1/ABCB1), and several UGT isoforms including UGT1A1 and UGT1A9 [8]. PXR activation by hyperforin is one of the strongest among any naturally occurring compound tested in human hepatocyte models [8].

This induction takes 7 to 14 days to reach full effect after starting St. John's Wort, and it persists for a similar washout period after stopping [9]. Low-hyperforin preparations (below 1% hyperforin) produce less induction, but standardization is poorly regulated in US supplements, and actual content varies widely between brands [9].

Documented Interactions With Similar Drugs

St. John's Wort has documented, clinically significant interactions with more than 50 drug classes. Several SGLT2-adjacent drugs illustrate the magnitude of risk. Co-administration of St. John's Wort reduced cyclosporine AUC by 52% in a prospective crossover study, leading to acute organ rejection in transplant patients [10]. It reduced midazolam AUC (a pure CYP3A4 substrate) by 54% in healthy volunteers [9]. Warfarin INR fell by a mean of 1.0 unit in patients taking concurrent St. John's Wort [11]. These are not theoretical signals. They are measured, clinically consequential reductions.

The Specific Interaction: St. John's Wort and Dapagliflozin

Pharmacokinetic Pathway Analysis

Dapagliflozin metabolism runs primarily through UGT1A9 (glucuronidation) and secondarily through CYP3A4 (oxidation) [5]. St. John's Wort induces both pathways via PXR activation [8]. Co-induction of UGT1A9 and CYP3A4 simultaneously would be expected to accelerate dapagliflozin clearance through both routes, compressing AUC more than induction of either pathway alone would predict.

No published dedicated pharmacokinetic study of the St. John's Wort plus dapagliflozin combination exists as of January 2025. The closest available data come from two sources. First, the rifampin interaction study in the Farxiga prescribing information: rifampin (a dual CYP3A4 and UGT1A9 inducer with potency broadly comparable to St. John's Wort for CYP3A4) reduced dapagliflozin AUC by approximately 22% [1]. Second, in vitro UGT1A9 induction data showing that hyperforin stimulates UGT1A9 transcription at concentrations achievable with standard OTC doses [8].

Combining these data streams, a conservative clinical estimate is a 20 to 25% reduction in dapagliflozin AUC with concurrent St. John's Wort use. This figure aligns with the FDA's general guidance that potent inducers of CYP3A4 and UGT1A9 reduce dapagliflozin exposure meaningfully [1].

Is This a Pharmacodynamic Interaction Too?

The interaction is primarily pharmacokinetic. There is no evidence that St. John's Wort directly antagonizes or agonizes SGLT2 receptors. However, a secondary pharmacodynamic consideration exists: St. John's Wort is used for mild-to-moderate depression, and untreated or worsening depression is associated with worse glycemic control and medication adherence in type 2 diabetes [12]. If St. John's Wort is being used as a mood support tool in a patient with comorbid depression and diabetes, abrupt discontinuation without a pharmacist- or physician-supervised plan carries its own risks.

What the FDA Prescribing Information Says

The FDA-approved Farxiga label states directly: "Inducers of UGT1A9: Rifampin decreased dapagliflozin AUC by 22%. Other inducers of UGT1A9 (e.g., mefenamic acid, diflunisal) or CYP3A4 may decrease the exposure of dapagliflozin" [1]. St. John's Wort is classified as a potent CYP3A4 inducer in the FDA Drug Interaction Studies guidance document [13] and as a UGT inducer in published clinical pharmacology literature [8]. The prescribing information does not list every inducer by name, but the pharmacological mechanism makes St. John's Wort directly relevant to this warning.

Clinical Consequences of Reduced Dapagliflozin Exposure

Glycemic Control

A 22 to 25% reduction in dapagliflozin AUC can translate to a measurable rise in HbA1c. In the dose-ranging study supporting Farxiga approval, the difference in HbA1c reduction between 5 mg and 10 mg dapagliflozin was approximately 0.2 to 0.3 percentage points [14]. A pharmacokinetic drop of similar magnitude from enzyme induction could produce a comparable glycemic loss, enough to push a well-controlled patient back above the ADA target of 7.0% [15].

Cardiovascular and Renal Protection

The cardio-renal benefits of dapagliflozin are time-averaged and exposure-dependent. DAPA-HF enrolled patients for a median of 18.2 months, and the survival curves diverged within weeks of starting treatment [3]. Any sustained reduction in drug exposure during that critical window may attenuate benefit. The DAPA-CKD trial similarly showed early divergence in eGFR slopes within the first 2 to 4 weeks [4]. Patients taking St. John's Wort chronically for depression are unlikely to be cycling on and off, meaning the exposure deficit compounds over months.

Urinary Glucose Excretion and Diabetic Ketoacidosis Risk

Lower dapagliflozin exposure means less urinary glucose excretion, which actually reduces one adverse effect: euglycemic diabetic ketoacidosis (DKA). Paradoxically, if a patient abruptly stops St. John's Wort after long-term use, enzyme induction reverses over 1 to 2 weeks, and dapagliflozin plasma levels may rise transiently above baseline. This rebound could theoretically increase glycosuria, fluid loss, and the risk of volume depletion or DKA in high-risk patients [16].

What to Do If You Are Already Taking Both

Step 1: Tell Your Prescriber Before Stopping

Do not abruptly discontinue either medication or supplement without medical guidance. Stopping St. John's Wort suddenly can cause a discontinuation-like reaction in some patients and, as noted above, causes enzyme induction to reverse, potentially increasing dapagliflozin exposure transiently [9].

Step 2: Check Your Glycemic Markers

If you have been taking both for more than 2 to 4 weeks, request an HbA1c and fasting glucose check. Compare to your most recent pre-combination values. A rise in HbA1c of 0.3 percentage points or more warrants a conversation about either discontinuing St. John's Wort or adjusting dapagliflozin dosing strategy [15].

Step 3: Discuss Evidence-Based Mood Support Alternatives

Several supplements with plausible benefit for mild depression carry no meaningful CYP3A4 or UGT induction. Omega-3 fatty acids (EPA-dominant, at 1 to 2 g EPA per day) showed modest antidepressant effects in a meta-analysis of 26 randomized controlled trials [17]. Saffron extract (30 mg/day standardized to safranal) reduced depressive symptoms versus placebo in a 2019 meta-analysis of 23 trials [18]. Neither compound induces CYP3A4 at typical doses [19]. Magnesium glycinate and vitamin D deficiency correction also carry no meaningful pharmacokinetic interaction risk and may support mood in deficient patients [20].

Step 4: If the Combination Continues

If a patient declines to stop St. John's Wort and the prescriber opts to continue dapagliflozin, the monitoring plan should include HbA1c every 6 to 8 weeks until stable, fasting plasma glucose at each visit, and consideration of whether a higher dapagliflozin dose (from 5 mg to 10 mg) would recover adequate exposure. Dose escalation is only viable within the approved dosing range and requires clinical judgment about tolerability, eGFR, and concurrent antihyperglycemic agents [1].

Who Is at Highest Risk From This Interaction?

Not every patient faces the same level of concern. Risk stratification helps guide urgency.

Higher Risk Patients

Patients on dapagliflozin 5 mg (the lower approved dose) start with less pharmacokinetic headroom. A 22 to 25% AUC reduction from that lower baseline brings plasma levels closer to the minimum effective concentration. Patients with HbA1c already near the top of their target range (6.8 to 7.0%) have little buffer before glycemic targets are breached [15]. Patients using Farxiga primarily for heart failure or CKD protection rather than glucose control face a different but equally real risk: erosion of cardiovascular endpoint benefit established in DAPA-HF and DAPA-CKD [3,4].

Lower Risk Patients

Patients on dapagliflozin 10 mg with well-controlled HbA1c well below 7.0% and no active heart failure or CKD may tolerate a 20 to 25% AUC reduction with minimal short-term clinical consequence, but monitoring remains warranted. A 2022 pharmacovigilance analysis of SGLT2 inhibitor drug interactions using the FDA Adverse Event Reporting System (FAERS) identified enzyme-inducer combinations as an underreported source of secondary glycemic failure [21].

What Healthcare Providers Should Know

Documentation and Counseling

The American Diabetes Association 2024 Standards of Care recommend that clinicians perform a thorough medication and supplement review at every diabetes visit, including herbal products [15]. St. John's Wort is frequently omitted from patient-reported medication lists because patients do not consider supplements to be "real drugs." Direct questioning ("Do you take any herbal teas, vitamins, or supplements from a health food store?") increases disclosure rates substantially [22].

Pharmacy Screening Limitations

Most pharmacy interaction-checking software flags St. John's Wort interactions with CYP3A4 substrates. However, dapagliflozin's primary metabolism through UGT1A9 means some algorithms may assign only a low-severity flag, underweighting the dual-pathway induction risk. Pharmacists reviewing Farxiga prescriptions should apply clinical judgment beyond the automated flag severity score.

Guideline Reference Point

The 2023 ADA/EASD consensus report on type 2 diabetes management states that "optimization of background pharmacotherapy is essential before attributing treatment failure to disease progression" [23]. Unrecognized supplement-drug interactions are a documented cause of apparent treatment failure, and identifying them should precede dose escalation or add-on therapy.

Summary of the Evidence Base

The table below organizes the key evidence tiers for this interaction.

| Evidence Type | Finding | Source | |---|---|---| | FDA prescribing information | Rifampin (dual UGT1A9/CYP3A4 inducer) reduced dapagliflozin AUC by 22% | Farxiga PI [1] | | In vitro pharmacology | Hyperforin induces UGT1A9 and CYP3A4 via PXR at therapeutic concentrations | Tirona et al. [8] | | Clinical analogue | St. John's Wort reduced midazolam (CYP3A4 substrate) AUC by 54% | Markowitz et al. [9] | | Clinical analogue | St. John's Wort reduced cyclosporine AUC by 52% | Ruschitzka et al. [10] | | Glycemic threshold | ADA target HbA1c <7.0%; 0.3% rise clinically meaningful | ADA 2024 [15] | | Cardio-renal outcomes | DAPA-HF: 26% reduction in HF/CV death with dapagliflozin 10 mg | McMurray et al. [3] |