Before they mix,
make them speak.

Effect: Acute kidney injury, reduced blood-pressure control, and electrolyte disturbance can occur, especially with dehydration.

Action: Avoid casual NSAID use. A clinician should review necessity, renal function, potassium, hydration, and sick-day planning.

Drain + block + squeeze = kidney risk.

Effect: Acute kidney injury, fluid retention, and blood-pressure worsening can occur.

Action: Avoid self-treatment and ask for a kidney-safe pain plan. Review sick-day risks during vomiting or diarrhea.

Dehydrated kidney + NSAID = danger.

Effect: Hyperkalemia may cause weakness, tingling, or a dangerous heart rhythm.

Action: Use only with a monitoring plan. Check potassium and kidney function after initiation and dose changes.

RAAS + K means recheck K.

Effect: Serious hyperkalemia can develop, particularly with kidney impairment or older age.

Action: Seek an alternative or arrange early potassium and renal monitoring through the prescriber.

TMP + K-raiser = potassium alert.

Effect: The risk of gastrointestinal and other serious bleeding rises.

Action: Do not self-start an NSAID. Ask a pharmacist or prescriber for a safer pain plan.

Thin blood + injure gut = bleed.

Effect: Major bleeding risk increases. The combination is sometimes intentional for a specific cardiovascular reason.

Action: Never add or stop either drug without confirming the indication and intended duration.

Two pathways, one bleed risk.

Effect: Bleeding risk may rise, especially with another antiplatelet drug or NSAID.

Action: Combination may be appropriate. Review other bleeding risks and counsel on warning signs.

Serotonin also matters to platelets.

Effect: Anticoagulant effect may increase quickly and cause bleeding.

Action: Contact the anticoagulation team before or promptly after starting. Extra INR checks and dose adjustment may be required.

New anti-infective? New INR plan.

Effect: INR may decrease and clot protection can be lost.

Action: Avoid unplanned use. Arrange close INR monitoring during initiation and again after discontinuation.

Inducer in, INR may go down.

Effect: Anticoagulant protection can be reduced and thrombosis risk may rise.

Action: Avoid the combination unless a specialist has selected and monitored it.

Speed the exit, lose the effect.

Effect: Large changes in vitamin K intake can change INR and warfarin effect.

Action: Do not eliminate healthy greens. Keep intake reasonably consistent and tell the anticoagulation team about major diet changes.

Consistent, not forbidden.

Effect: A sudden dangerous rise in blood pressure can occur. This is mainly hypertensive crisis, not serotonin syndrome.

Action: Follow the exact medicine-specific tyramine diet and seek urgent help for severe symptoms.

MAOI + aged/fermented = pressure crisis.

Effect: Exposure to some CYP3A substrates can rise, sometimes substantially.

Action: Check the exact product monograph. Separating by a few hours may not solve the interaction.

Grapefruit changes the gut gate.

Effect: Motor response may become delayed or less predictable in some patients.

Action: Keep meal timing consistent and discuss protein redistribution with the Parkinson care team if wearing-off is meal-related.

Protein and levodopa share a doorway.

Effect: Product labelling warns of nausea, vomiting, flushing, headache, and abdominal symptoms.

Action: Follow the product monograph and avoid alcohol during treatment and for the labelled interval afterward.

Metronidazole course means alcohol pause.

Effect: Bleeding risk can increase. The exact effect varies by DOAC, dose, kidney function, and inhibitor.

Action: Verify the exact product monograph. Avoid, adjust, or monitor only under a clinician’s plan.

Block the exit, raise the level.

Effect: Lithium concentrations can rise, sometimes after an apparently small medication change.

Action: Avoid self-starting NSAIDs. Arrange lithium level, renal function, symptoms, and dose review after changes.

Kidney change means lithium change.

Effect: Myopathy and rhabdomyolysis risk can increase, particularly with simvastatin.

Action: Verify the statin-specific monograph. A temporary hold, dose limit, or alternative may be needed.

Block CYP3A, statin level climbs.

Effect: Bradycardia, conduction problems, and digoxin toxicity can occur.

Action: Review digoxin dose, kidney function, electrolytes, level timing, and pulse monitoring.

Block P-gp, digoxin backs up.

Effect: Profound hypotension, bradycardia, and excessive sedation can occur.

Action: Avoid the combination and select an alternative.

Tizanidine + cipro is a no-go pair.

Effect: Nausea, tremor, tachycardia, seizures, and arrhythmias can occur.

Action: Avoid or arrange dose reduction and serum concentration monitoring.

CYP1A2 blocked, theophylline climbs.

Effect: The risk of serious rash and neurologic adverse effects increases.

Action: Use the valproate-specific slow lamotrigine titration. Never restart at the old dose after a significant interruption without advice.

Valproate means slower lamotrigine.

Effect: Profound sedation, slowed breathing, coma, and death can occur.

Action: Use together only when specifically coordinated. Confirm naloxone access and an individualized safety plan.

Two brakes can stop breathing.

Effect: Sedation, falls, and respiratory depression can increase.

Action: Review dose, kidney function, other sedatives, and naloxone need. Avoid alcohol.

Pain stack can become a breathing stack.

Effect: Impaired judgment, falls, overdose, and respiratory depression can occur.

Action: Avoid alcohol with opioids and sedatives unless a clinician has given specific advice.

Sedative + alcohol = stronger than either.

Effect: Drowsiness, confusion, falls, and impaired driving increase, especially in older adults.

Action: Avoid duplicate sedatives and do not drive until effects are known.

Night-time label can hide daytime risk.

Effect: Severe serotonin toxicity can develop. Drug-specific washout periods matter.

Action: Avoid unless a specialist is managing the exact combination or transition. Severe or rapidly worsening symptoms require emergency care.

MAOI + serotonin is the red line.

Effect: Serotonin toxicity can develop, especially when tramadol, dextromethorphan, St. John’s wort, or a serotonin precursor joins an antidepressant.

Action: Avoid self-starting the second agent. Verify necessity, dose, alternatives, and symptom counselling.

Serotonin stacks. Clonus is the clue.

Effect: Serotonin toxicity is possible but less common than with tramadol or meperidine. Higher opioid exposure may raise risk.

Action: Combination may be appropriate with monitoring. Counsel on the symptom pattern and review perioperative or dose changes.

Not every opioid has the same serotonin risk.

Effect: Serotonin toxicity risk rises, although some combinations are intentionally prescribed.

Action: Use only with a prescriber-managed plan and monitor closely after starts, switches, and dose increases.

Intentional does not mean invisible. Monitor the stack.

Effect: Risk of torsades de pointes and a dangerous ventricular rhythm rises with multiple QT-prolonging drugs.

Action: Confirm necessity, dose, ECG need, electrolytes, renal function, and other risk factors.

QT + QT needs an ECG question.

Effect: Low potassium or magnesium, dehydration, or existing long-QT risk can make arrhythmia more likely.

Action: Seek clinical review of ECG and electrolytes, particularly during vomiting, diarrhea, or acute illness.

QT risk lives in the patient too.

Effect: Blood pressure can fall to a dangerous level.

Action: Do not combine. Emergency clinicians must know when the PDE5 inhibitor was last taken.

Nitrate + ED drug = pressure crash.

Effect: Symptomatic hypotension and falls can occur.

Action: A prescriber should coordinate stable dosing, low starting doses, and timing.

Two vessel relaxers, one pressure drop.

Effect: Severe marrow suppression, mouth sores, infection, kidney injury, and folate toxicity can occur.

Action: Avoid unless a specialist intentionally manages the combination. Seek urgent assessment for toxicity symptoms.

Two folate blockers can shut down marrow.

Effect: Methotrexate toxicity risk may rise, especially at higher doses or with kidney impairment.

Action: Do not self-start an NSAID. Verify dose, indication, renal function, and monitoring plan.

Methotrexate exits by kidney. Protect the exit.

Effect: Hormone exposure can fall and pregnancy risk can increase.

Action: Use a guideline-supported alternative or backup method for the required duration during and after the inducer.

Inducer speeds hormones away.

Effect: Thyroid control may worsen if calcium, iron, or antacids bind levothyroxine.

Action: Separate according to the product monograph, commonly by at least four hours, and keep the routine consistent.

Thyroid first. Minerals later.

Effect: Antibiotic exposure and treatment effectiveness can fall.

Action: Use the exact drug-specific spacing instructions. The interval differs by antibiotic.

Cations capture certain antibiotics.

Effect: Food, minerals, and other medicines can nearly eliminate absorption.

Action: Take with plain water on an empty stomach, remain upright, and wait for the monograph-specified interval before food or other medicines.

Alendronate travels alone.

Effect: Delayed hypoglycemia can occur, especially without food or after exercise.

Action: Avoid binge drinking and drinking on an empty stomach. Follow an individualized glucose-monitoring and treatment plan.

Alcohol can block the liver’s glucose rescue.

Effect: Palpitations and tremor may be blunted, making low glucose harder to recognize.

Action: Use glucose readings and teach alternative symptoms. Do not stop the beta blocker abruptly.

The low is real even when the heart stays quiet.