Can I Take St John's Wort with Jardiance (Empagliflozin)?

How Empagliflozin Is Metabolized

Empagliflozin (Jardiance) is primarily metabolized via glucuronidation by UGT1A3, UGT1A8, UGT1A9, and UGT2B7, with minor involvement of CYP3A4. The FDA prescribing information for empagliflozin confirms that CYP3A4 contributes a secondary but measurable route of clearance. P-glycoprotein (P-gp) also acts as an efflux transporter that limits intestinal absorption of the drug. [1]

UGT Glucuronidation as the Primary Route

UGT enzymes account for the majority of empagliflozin's phase II metabolism, producing three glucuronide metabolites (M2, M4, M5) that are pharmacologically inactive. This means direct UGT inducers pose a larger theoretical risk to Jardiance than CYP3A4 inducers alone. St John's Wort does not meaningfully induce UGT1A9, which is the dominant UGT isoform here. [2]

The Secondary CYP3A4 and P-gp Route

Even though CYP3A4 is a secondary path, studies of other SGLT2 inhibitors show that combined CYP3A4 and P-gp induction can reduce systemic drug exposure. The FDA drug interaction guidance for SGLT2 inhibitors lists CYP3A4/P-gp inducers as requiring monitoring or dose review. [3] St John's Wort is one of the strongest known herbal inducers of both pathways.

Why St John's Wort Is a Strong Enzyme Inducer

St John's Wort contains two classes of active compounds: naphthodianthrones (primarily hypericin) and phloroglucinols (primarily hyperforin). Hyperforin is the constituent responsible for CYP enzyme induction, acting as a ligand for the pregnane X receptor (PXR), which then upregulates transcription of CYP3A4, CYP2C9, and the drug efflux pump P-glycoprotein. [4]

Magnitude of Induction in Clinical Studies

A 2000 study published in The Lancet by Piscitelli et al. Documented that St John's Wort reduced indinavir (a CYP3A4 substrate) plasma AUC by 57% after 14 days of co-administration. [5] For cyclosporine, another CYP3A4/P-gp substrate, St John's Wort reduced trough levels by 40 to 70% in transplant recipients, leading to acute rejection episodes. [6]

These numbers come from drugs that are more dependent on CYP3A4 than empagliflozin is. The reduction in Jardiance exposure would likely be smaller, but the direction of the effect is the same: lower plasma drug concentration and potentially less glucose lowering.

Hyperforin Content Drives Variability

Not all St John's Wort products are equal. Standardized extracts (e.g., LI 160, WS 5570) contain 3 to 5% hyperforin and produce the most pronounced induction. Low-hyperforin preparations (<0.5% hyperforin) cause minimal PXR activation. Most products sold in the United States are not standardized for hyperforin content, making the actual induction unpredictable. A 2004 review in Clinical Pharmacokinetics documented that hyperforin content, not hypericin content, drives the majority of drug interactions observed with St John's Wort. [7]

Pharmacokinetic Impact on Empagliflozin Specifically

No published randomized crossover trial has tested St John's Wort co-administration directly with empagliflozin. This is an important gap. What does exist is:

1. Empagliflozin's pharmacokinetic profile from the EMPA-REG OUTCOME trial and the FDA label.
2. Mechanistic data on CYP3A4/P-gp induction from St John's Wort.
3. Class-level SGLT2 inhibitor interaction data from canagliflozin and dapagliflozin studies.

What the Empagliflozin Label Says

The Jardiance FDA prescribing information states that co-administration with rifampicin, a potent CYP3A4/P-gp inducer comparable in mechanism to St John's Wort, reduced empagliflozin AUC by approximately 35% and Cmax by approximately 22%. [1] This is a clinically relevant reduction. At the 10 mg dose, a 35% AUC drop moves the plasma exposure closer to the threshold at which urinary glucose excretion and HbA1c benefit diminish.

Class Evidence From Dapagliflozin

Dapagliflozin (Farxiga), another SGLT2 inhibitor with a similar but not identical metabolic profile, showed a 22% reduction in AUC when co-administered with rifampicin in a dedicated pharmacokinetic study. The FDA dapagliflozin label notes that strong CYP3A4 inducers may reduce efficacy. [8] St John's Wort's induction potency is generally considered comparable to rifampicin for CYP3A4, though somewhat less potent for P-gp.

Estimated Clinical Impact on Glycemic Control

If a 35% AUC reduction (as seen with rifampicin) applies to the 10 mg Jardiance dose, effective plasma exposure becomes equivalent to roughly 6.5 mg. No approved 6.5 mg dose exists. The EMPA-REG OUTCOME trial enrolled 7,020 patients and showed that empagliflozin 10 mg reduced HbA1c by approximately 0.54% versus placebo at 12 weeks. [9] A meaningful drop in systemic exposure could erase part of that glycemic benefit, particularly in patients near their HbA1c target.

Clinical Risk Assessment: Who Is Most Vulnerable

Not every Jardiance patient faces equal risk from St John's Wort co-use.

Patients at Higher Risk

Patients on 10 mg empagliflozin (rather than 25 mg) have less pharmacokinetic buffer. Patients using Jardiance primarily for glycemic control in type 2 diabetes, rather than for heart failure or CKD reduction, may notice the glycemic impact first. Patients already near their upper HbA1c threshold (e.g., HbA1c 7.8 to 8.2%) face a greater clinical consequence if glucose control deteriorates.

Patients on Jardiance for Heart Failure or CKD

The EMPEROR-Reduced trial (N=3,730) showed empagliflozin reduced the composite of cardiovascular death or hospitalization for heart failure by 25% versus placebo. [10] If enzyme induction reduces plasma exposure substantially, the cardioprotective and renoprotective benefits may also be compromised, though no direct evidence currently proves this for the St John's Wort combination specifically.

Patients Taking Both Unknowingly

St John's Wort is available over-the-counter in the United States. A CDC National Health Interview Survey analysis found that approximately 18% of U.S. Adults taking prescription medications also use herbal supplements without disclosing this to their prescriber. [11] This makes proactive screening at every diabetes visit clinically relevant.

The Pharmacodynamic Angle: Does St John's Wort Affect Blood Sugar?

Beyond the pharmacokinetic interaction, St John's Wort carries a secondary concern: it may independently alter glucose metabolism. A 2013 study in Phytomedicine found that hyperforin inhibits glucocorticoid signaling pathways that influence hepatic glucose production in animal models, though human clinical data remain limited. [12] The net glycemic direction in humans is not well established.

Serotonin and Insulin Secretion

Serotonin plays a role in pancreatic beta-cell function. St John's Wort acts as a serotonin reuptake inhibitor, and a 2017 paper in Diabetes Care noted associations between serotonergic signaling and insulin secretion from beta cells. [13] Whether St John's Wort's serotonergic activity translates to any measurable insulin secretion effect in diabetic patients on SGLT2 inhibitors has not been studied. The theoretical risk does not justify use when safer alternatives exist.

What to Do If You Are Already Taking Both

If a patient presents already combining St John's Wort with Jardiance, the following practical steps apply:

Step 1: Assess Duration of Co-Use

Full CYP3A4 induction from St John's Wort develops over 7 to 14 days of consistent use. If co-use has been less than one week, induction may be incomplete. Check current fasting glucose and compare to baseline.

Step 2: Check Recent HbA1c

If HbA1c has risen since starting St John's Wort, and no other changes in diet, activity, or dose occurred, the interaction is a plausible contributor. The American Diabetes Association Standards of Care 2024 recommends reviewing all medications, supplements, and herbal products as part of routine diabetes management. [14]

Step 3: Prioritize Discontinuing St John's Wort

The safer option is stopping the herbal supplement, not adjusting the prescription drug dose. CYP3A4 induction resolves within approximately two weeks of stopping St John's Wort. Fasting glucose should be rechecked 2 to 3 weeks after discontinuation to confirm return to prior levels.

Step 4: Seek an Alternative for the Underlying Indication

St John's Wort is most commonly taken for mild to moderate depression. The American Academy of Family Physicians acknowledges evidence supporting St John's Wort for mild depression but notes its interaction profile limits use in patients on prescription regimens. [15] Escitalopram, sertraline, or bupropion prescribed by a physician do not induce CYP3A4 and are not expected to alter empagliflozin exposure.

Monitoring Parameters If the Combination Cannot Be Avoided

In rare cases where a patient refuses to discontinue St John's Wort, monitoring becomes the management strategy.

Glucose Monitoring Schedule

• Fasting glucose: weekly for the first 4 weeks after starting St John's Wort
• HbA1c: recheck at 3 months rather than the standard 6-month interval
• Symptoms of hyperglycemia: increased thirst, polyuria, fatigue, blurred vision

Dose Adjustment Consideration

Empagliflozin's maximum approved dose is 25 mg once daily. If the patient is on 10 mg and glucose control clearly deteriorates after starting St John's Wort, the prescriber may consider increasing to 25 mg, then reassessing after the herbal is stopped. No published protocol exists for this scenario. Any dose change requires individualized clinical judgment based on renal function (eGFR must be >30 mL/min/1.73m² for continued empagliflozin use) and cardiovascular profile. [1]

Disclosing Supplements to Your Diabetes Care Team

The interaction between St John's Wort and Jardiance illustrates a broader problem: the assumption that "natural" products are inherently safe alongside prescription drugs. Hypericum perforatum has documented interactions with cyclosporine, warfarin, HIV protease inhibitors, oral contraceptives, digoxin, and multiple antiretrovirals. A 2004 systematic review in the American Journal of Medicine identified 108 case reports and pharmacokinetic studies demonstrating clinically significant interactions between St John's Wort and prescription drugs. [16]

Empagliflozin's prescribing information explicitly lists rifampicin (the canonical CYP3A4/P-gp inducer) as reducing AUC by 35%, making it the reference comparator for any discussion of herbal induction. [1] St John's Wort belongs in the same category of clinical concern.

Bring a complete list of all supplements, vitamins, and herbal products to every diabetes appointment. Photograph the labels or bring the bottles. Your prescriber cannot screen for interactions from information they do not have.