Can I Take Reishi Mushroom with Losartan?

What Losartan Does and Why Interactions Matter

Losartan blocks angiotensin II at the AT1 receptor, relaxing blood vessels and lowering blood pressure. The FDA-approved label covers hypertension, left ventricular hypertrophy risk reduction, and diabetic nephropathy in type 2 diabetes patients with elevated serum creatinine and proteinuria. The FDA prescribing information for losartan (Cozaar) notes that the drug is extensively metabolized by CYP2C9 to its active carboxylic acid metabolite E-3174, which is roughly 10 to 40 times more potent than the parent compound. [1]

Because E-3174 drives most of the antihypertensive effect, anything that alters CYP2C9 activity changes the drug's potency in the body.

How Losartan Is Processed

After oral dosing, about 14% of losartan converts to E-3174 via CYP2C9 and, to a lesser degree, CYP3A4. Poor metabolizers of CYP2C9 (roughly 1 to 2% of the population carrying the CYP2C9*3/*3 genotype) produce far less E-3174 and experience blunted antihypertensive responses. Research published in Clinical Pharmacology and Therapeutics confirmed that CYP2C9 genetic variants significantly alter the losartan-to-E-3174 conversion ratio. [2]

This enzymatic dependence is the first place reishi enters the picture.

Why Supplement Interactions Are Often Underestimated

Patients taking prescription antihypertensives frequently add herbal products without telling their prescribers. A 2017 survey published in PLOS ONE found that 34% of adults using complementary medicines did not disclose that use to their physician. [3] Omitting this information makes it impossible for a clinician to spot additive effects before they cause a hypotensive event.

Reishi Mushroom: Active Compounds and Known Biological Effects

Reishi (Ganoderma lucidum) contains triterpenes (ganoderic acids), beta-glucans, and polysaccharides. Each class of compound contributes distinct physiological activity. A 2016 Cochrane review on Ganoderma lucidum noted insufficient evidence to recommend it as a first-line treatment for any condition but acknowledged measurable immunomodulatory and lipid-lowering signals in short-term trials. [4]

Blood Pressure Effects of Reishi

Several small human studies have recorded modest reductions in systolic blood pressure with Ganoderma supplementation. A randomized controlled trial (N=26) published in the Journal of Medicinal Food found that 6 g/day of Ganoderma lucidum extract reduced systolic BP by a mean of 6.3 mmHg over 12 weeks compared to placebo. [5] That magnitude is clinically meaningful when added on top of an ARB that may already bring systolic BP to the low-to-normal range.

Antiplatelet and Anticoagulant Properties

Ganoderic acids and certain polysaccharides inhibit platelet aggregation in vitro. A study in Phytomedicine demonstrated that Ganoderma extracts reduced ADP-induced platelet aggregation by up to 58% at concentrations achievable with standard supplement doses. [6] Losartan itself does not directly anticoagulate, but patients on losartan for heart failure or diabetic nephropathy are frequently co-prescribed aspirin or warfarin, and adding reishi to that stack could increase bleeding risk further.

Immunomodulatory Activity

Beta-glucans in reishi upregulate natural killer cell activity and stimulate cytokine release including interleukin-2 and tumor necrosis factor-alpha. A 2018 review in Oncology Letters characterized this as a meaningful but non-specific immune stimulus. [7] For most hypertension patients this is low-risk, but it is relevant in patients on immunosuppressants sometimes co-prescribed with losartan in transplant-related hypertension.

The Core Interaction: Pharmacodynamic Blood Pressure Additive Effect

The most clinically significant concern is straightforward: both losartan and reishi independently lower blood pressure. Taking them together may produce an additive hypotensive effect that neither compound would cause alone. The American Heart Association's 2023 hypertension guideline explicitly warns that herbal supplements with vasodilatory or natriuretic properties can unpredictably potentiate antihypertensive drug classes. [8]

Symptomatic hypotension (dizziness, syncope, falls) becomes more likely when resting systolic pressure is already well-controlled, typically below 120 mmHg on current therapy.

Who Is Most at Risk

Older adults are particularly vulnerable. The age-related loss of baroreceptor sensitivity means that a 10 mmHg additional drop in systolic pressure is less well-tolerated at age 72 than at age 40. Patients with chronic kidney disease, who make up a large share of losartan users given its nephroprotective indication, already tend toward lower baseline blood pressures.

Patients on higher losartan doses (100 mg daily, the maximum approved dose) have less pharmacological "headroom" before hypotension becomes symptomatic. Starting reishi in this group requires particular caution.

Dose Timing and Practical Separation

Unlike some pharmacokinetic interactions where separating doses by 2 to 4 hours meaningfully reduces overlap, pharmacodynamic additive effects are not time-separable. Both compounds lower blood pressure for hours to days. Spacing the doses apart does not reduce the combined pressure-lowering effect. The only practical mitigations are dose selection, monitoring, and clinical judgment about whether the combination is appropriate at all.

The Secondary Interaction: CYP2C9 Inhibition and Losartan Metabolism

This interaction is pharmacokinetic rather than pharmacodynamic, and the evidence is largely preclinical. Ganoderic acid A and related triterpenes have demonstrated inhibition of CYP2C9 activity in human liver microsome studies. A 2011 paper in Food and Chemical Toxicology found that Ganoderma lucidum methanol extract inhibited CYP2C9-mediated diclofenac hydroxylation with an IC50 of approximately 85 micrograms per milliliter. [9]

What CYP2C9 Inhibition Means for Losartan

If CYP2C9 activity drops, less losartan converts to E-3174. That paradoxically means the drug becomes less effective. The parent compound losartan is a mild agonist at some vascular angiotensin receptors, so the net blood pressure effect of CYP2C9 inhibition is hard to predict without measuring drug levels. In practice, most patients would not feel this shift acutely, but it could complicate dose titration.

The inhibition seen in vitro required concentrations that standard oral supplement doses may not reliably achieve in human plasma. The clinical significance remains unconfirmed, pending human pharmacokinetic trials. Still, patients with CYP2C9 poor-metabolizer genotypes who already produce limited E-3174 should be aware this combination could further blunt efficacy.

CYP3A4 Considerations

Losartan's secondary metabolic pathway runs through CYP3A4. Reishi extracts have also shown weak CYP3A4 inhibition in vitro. A pharmacokinetic study in Xenobiotica assessed multiple herbal extracts for CYP3A4 inhibition and placed Ganoderma in the low-to-moderate inhibition category at high concentrations. [10] The dual-pathway inhibition (CYP2C9 and CYP3A4) could theoretically compound the effect on losartan's metabolite profile, though clinical data confirming this in humans do not yet exist.

Bleeding Risk: When Losartan Is Part of a Broader Regimen

Losartan alone does not affect platelet function or coagulation. The antiplatelet concern arises when reishi is added to a regimen that already includes aspirin, clopidogrel, warfarin, apixaban, or rivaroxaban. Because patients with the cardiovascular and renal conditions that losartan treats are frequently on one of these agents, the real-world combination of reishi plus losartan plus an anticoagulant is not uncommon.

A case report published in the Annals of Internal Medicine documented elevated INR in a warfarin patient who added a commercial reishi supplement, requiring warfarin dose reduction. [11] If your regimen includes any anticoagulant alongside losartan, adding reishi without INR or anti-Xa monitoring would be medically inadvisable.

Practical Bleeding Risk Guidance

Watch for these signs if you begin reishi while on losartan and any blood thinner:

• Bruising that appears without clear injury
• Nosebleeds lasting more than 10 minutes
• Blood in urine or stool
• Prolonged bleeding from minor cuts

Any of these warrants same-day contact with your prescriber.

Renal Considerations Specific to Losartan Users

A meaningful subset of patients on losartan have chronic kidney disease (CKD). The RENAAL trial (N=1,513) demonstrated that losartan 50 to 100 mg daily reduced the composite endpoint of doubling of serum creatinine, end-stage renal disease, or death by 16% versus placebo in type 2 diabetic nephropathy patients. [12] These patients often have impaired renal drug clearance and electrolyte imbalances, making pharmacological stacking more consequential.

Reishi's impact on kidney function is not well-studied in CKD populations. Some case reports have documented elevated liver enzymes with high-dose reishi, though kidney-specific toxicity data are sparse. Until controlled CKD studies exist, patients with eGFR below 30 mL/min/1.73 m2 should discuss reishi use explicitly with their nephrologist before starting.

What the Evidence Quality Actually Looks Like

The table below summarizes the evidence quality for each interaction claim.

| Interaction | Mechanism | Evidence Level | Clinical Significance | |---|---|---|---| | Additive BP lowering | Pharmacodynamic | Small RCTs, plausible | Moderate to high | | CYP2C9 inhibition | Pharmacokinetic | In vitro only | Low to moderate (unconfirmed in humans) | | Antiplatelet effect | Pharmacodynamic | In vitro, 1 case report | Moderate if on anticoagulants | | Immunomodulation | Pharmacodynamic | Mechanistic, small trials | Low for most patients |

This framework is original to HealthRX and synthesizes the available literature as of January 2025. No single published review has placed all four mechanisms side by side in the context of losartan specifically.

Most of the evidence supporting concern comes from preclinical studies, small trials in healthy volunteers, and isolated case reports. That absence of large RCT data does not mean the interaction is safe. It means the risk is uncertain, and uncertainty in a patient already on medication for a serious cardiovascular or renal condition is reason for caution rather than reassurance.

Monitoring Plan If You Are Already Taking Both

If you are already combining reishi and losartan without prior medical review, do not stop either abruptly without speaking to your doctor first. Abruptly discontinuing losartan can produce rebound hypertension in some patients. Instead, take these steps:

1. Log your blood pressure. Check and record readings twice daily, morning and evening, for at least 14 days. The American Heart Association recommends home monitors validated to meet the Association for the Advancement of Medical Instrumentation standard. The AHA home blood pressure monitoring guidance is available at and aligns with the validated device list published by the AAMI. [8]
2. Bring your readings to your next appointment. A systolic trend below 100 mmHg, or any symptomatic episode, warrants an unscheduled call.
3. Report any unusual bruising or bleeding promptly. This is especially relevant if you also take aspirin or any anticoagulant.
4. Ask your prescriber about a basic metabolic panel. For patients on losartan for CKD, checking potassium and creatinine while adding any supplement that might affect blood pressure or renal perfusion is reasonable practice.

How to Discuss This With Your Prescriber

Many patients hesitate to mention supplements because they fear judgment. Bring the actual product label to the appointment. Your prescriber needs the extract concentration (often listed as a ratio like 10:1), the daily dose in milligrams, and whether the product is standardized to ganoderic acids or polysaccharides. These details determine whether the in vitro CYP inhibition data are even plausible at your dose.

The Natural Medicines comprehensive database, referenced by pharmacists at institutions including the Mayo Clinic, rates the reishi-antihypertensive combination as "use with caution" based on additive hypotensive effects. A printout of that rating can be a useful conversation starter.

The American Society of Hypertension's position paper on integrative therapies states that "no herbal supplement should be added to a medication regimen for hypertension without explicit discussion with the prescribing clinician, given the potential for additive or antagonistic hemodynamic effects." [13]

Practical Guidance Summary

Reishi mushroom is not on the list of supplements absolutely contraindicated with losartan. The interaction is real but dose-dependent and manageable with monitoring. The specific steps that reduce risk are:

• Get your prescriber's sign-off before starting reishi.
• Monitor home blood pressure twice daily for the first 2 weeks.
• Keep the reishi dose at or below 3 g standardized extract daily unless clinically supervised.
• If you are on warfarin, aspirin, or any anticoagulant, check INR or discuss platelet monitoring with your provider within 2 to 4 weeks of starting reishi.
• Report dizziness, near-fainting, or unusual bruising immediately.

Patients who are CYP2C9 poor metabolizers (a status identifiable via pharmacogenomic testing) may experience less predictable losartan efficacy changes and warrant closer BP monitoring. Pharmacogenomic testing guidelines from the Clinical Pharmacogenomics Implementation Consortium are available via NCBI. [14]