Turmeric

Curcumin inhibits platelet aggregation via inhibition of thromboxane B2 and increases prostacyclin synthesis, producing antiplatelet effects additive with warfarin anticoagulation. At high doses, curcumin may inhibit CYP2C9, potentially reducing S-warfarin metabolism and elevating plasma warfarin levels. Multiple case reports exist of elevated INR in patients combining turmeric/curcumin with warfarin.

Advise patients on warfarin to avoid high-dose turmeric/curcumin supplements (>1g curcuminoids/day). If combined, monitor INR weekly initially. Culinary turmeric use is lower risk. Discontinue turmeric supplements 2 weeks before surgery.

Curcumin inhibits CYP2D6 activity in vitro and in some in vivo studies, reducing metabolism of CYP2D6-dependent substrates. For codeine (requires CYP2D6 activation to morphine), inhibition may reduce analgesia. For direct substrates like metoprolol, tramadol, or haloperidol, inhibition increases plasma levels and risk of adverse effects.

Use caution with high-dose curcumin in patients on narrow-TI CYP2D6 substrates. For codeine, inhibition may reduce analgesic efficacy; consider alternative analgesics. For metoprolol, monitor heart rate and blood pressure. For tramadol, monitor for CNS toxicity.

Curcumin modulates P-glycoprotein and multiple CYP enzymes, potentially altering chemotherapy drug bioavailability. In vitro, curcumin sensitizes cancer cells to doxorubicin. However, curcumin's antioxidant properties may theoretically reduce the oxidative stress mechanism of some chemotherapy agents. The net clinical effect is uncertain and context-dependent.

Patients undergoing active chemotherapy should discuss curcumin/turmeric supplement use with their oncologist before starting. Avoid high-dose curcumin during chemotherapy without specific oncology guidance. The potential to enhance or reduce drug efficacy is real but unpredictable.

Curcumin improves insulin sensitivity and reduces fasting blood glucose through activation of AMPK, PPAR-gamma, and inhibition of NF-κB-mediated inflammation. Clinical trials show curcumin supplementation improves HbA1c and fasting glucose in type 2 diabetics. This glucose-lowering effect is additive with metformin and other antidiabetics.

When turmeric is added to metformin therapy, monitor blood glucose more frequently for hypoglycemia, especially at curcumin doses >2g/day. The combination may allow dose reduction of metformin in some patients. This is generally a beneficial interaction but requires monitoring.

A published case report describes acute nephrotoxicity in a renal transplant patient who consumed turmeric (curcumin) supplements concurrently with tacrolimus. Curcumin inhibits CYP3A4 and P-glycoprotein, increasing tacrolimus bioavailability and plasma levels. Tacrolimus has an extremely narrow therapeutic index; elevated levels cause nephrotoxicity, neurotoxicity, and opportunistic infections.

Turmeric supplements are contraindicated in transplant patients on tacrolimus or cyclosporine. Standard culinary turmeric is lower-risk but should be used cautiously. Screen all transplant patients for curcumin/turmeric supplement use. Monitor tacrolimus trough levels and renal function closely.

Curcumin inhibits platelet aggregation via suppression of thromboxane B2 synthesis, PAF-receptor antagonism, and phospholipase A2 inhibition. NSAIDs also reduce platelet aggregation via COX-1 inhibition of thromboxane A2. Concurrent use produces additive antiplatelet effects and increases risk of GI bleeding — both agents independently cause gastric mucosal injury and combined use is synergistically ulcerogenic.

Avoid combining high-dose turmeric/curcumin supplements with NSAIDs for prolonged periods, particularly in patients with GI risk factors. If used together, monitor for GI bleeding symptoms (dark stools, haematemesis) and abnormal bruising. Prefer the shortest effective NSAID duration and lowest dose. Consider gastroprotection (PPI) if concurrent use is necessary.

SSRIs inhibit platelet serotonin reuptake, impairing platelet activation and increasing bleeding risk. Curcumin independently inhibits platelet aggregation via thromboxane and PAF pathways. Combined use produces additive antiplatelet effects. Additionally, curcumin modulates serotonergic neurotransmission and may have additive antidepressant effects, with theoretical risk of serotonin excess at high doses.

Monitor for unusual bleeding (easy bruising, epistaxis, prolonged wound bleeding) when turmeric/curcumin supplements are used alongside SSRIs. The antiplatelet interaction may be clinically significant particularly in patients also on anticoagulants. A pilot RCT showed curcumin as an antidepressant add-on — inform the prescribing psychiatrist of supplementation.

Curcumin improves insulin sensitivity through AMPK activation, PPAR-gamma agonism, and anti-inflammatory mechanisms in adipose and hepatic tissue. Multiple RCTs demonstrate glucose-lowering effects of curcumin supplementation in type 2 diabetes. Additive pharmacodynamic blood glucose reduction is well-supported, with potential for clinically significant hypoglycaemia if antidiabetic doses are not adjusted.

Monitor blood glucose more frequently when adding high-dose curcumin supplements to antidiabetic regimens. Educate patients on signs of hypoglycaemia (shakiness, diaphoresis, confusion). The combination may be synergistically beneficial (improved glycaemic control), but antidiabetic medication dose adjustment may be required in responsive patients. Consult the prescribing physician before starting high-dose curcumin.

Curcumin has demonstrated vasodilatory and antihypertensive properties in clinical studies, mediated through nitric oxide enhancement, antioxidant effects on vascular endothelium, and ACE inhibitory activity. Concurrent use with antihypertensive medications may produce additive blood pressure lowering, particularly at higher curcumin doses.

Monitor blood pressure when high-dose curcumin is added to antihypertensive regimens. Alert patients to symptoms of hypotension (dizziness, lightheadedness, syncope on standing). Standard dietary turmeric intake is unlikely to produce meaningful interactions, but medicinal curcumin extracts (500-4000 mg/day) warrant blood pressure monitoring.

Curcumin inhibits CYP2C19 in vitro, the primary enzyme responsible for the metabolism of most proton pump inhibitors (PPIs). CYP2C19 inhibition may increase PPI plasma concentrations and area under the curve, potentially enhancing acid suppression and increasing risk of PPI-related adverse effects (hypomagnesaemia, Clostridioides difficile infection, vitamin B12 deficiency with long-term use).

Clinically significant interaction is unlikely at standard curcumin doses given its low oral bioavailability. However, in patients on long-term high-dose PPI therapy combined with curcumin supplements, monitor for signs of PPI over-exposure. CYP2C19 poor metabolisers may be at greater risk. No dose adjustment is routinely required.