Farxiga (dapagliflozin) has several important drug interactions, though few are absolute prohibitions. The biggest risks involve medications that compound its effects on blood sugar, blood pressure, fluid balance, or kidney function. Knowing which combinations require caution can help you avoid dangerous side effects like dangerously low blood sugar, severe dehydration, or a rare but serious condition called ketoacidosis.
Insulin and Sulfonylureas
The most common interaction involves other diabetes medications that lower blood sugar directly. Farxiga works by flushing excess glucose out through your urine, so stacking it with insulin or sulfonylureas (like glipizide or glimepiride) can push blood sugar too low. The FDA label specifically warns that a lower dose of insulin or a sulfonylurea may be needed when you start Farxiga.
This doesn’t mean you can’t take them together. Many people do. But your doctor will likely reduce your insulin dose or sulfonylurea when adding Farxiga to prevent hypoglycemia, especially in the first few weeks. Watch for shakiness, sweating, confusion, or dizziness, which are signs your blood sugar has dropped too far.
Diuretics (Water Pills)
Farxiga acts as a mild diuretic on its own. It causes your kidneys to excrete extra sodium and water along with glucose, which typically produces a modest blood pressure drop of about 2 to 5 points systolic. That effect is usually harmless by itself, but combining Farxiga with loop diuretics (like furosemide) or thiazides (like hydrochlorothiazide) can amplify fluid loss enough to cause problems.
The main risks are orthostatic hypotension (a blood pressure drop when you stand up, which can cause dizziness or fainting), dehydration, and in some cases acute kidney injury. These risks are higher if you’re over 65, already have reduced kidney function, or are dealing with an illness that causes vomiting or diarrhea. In older adults, the combined diuretic effect can also worsen urinary incontinence, which itself increases fall risk.
If you’re on a stable diuretic regimen and starting Farxiga, your doctor may lower your diuretic dose or reduce other blood pressure medications to compensate.
NSAIDs Like Ibuprofen and Naproxen
Over-the-counter pain relievers like ibuprofen (Advil) and naproxen (Aleve) deserve extra caution while you’re on Farxiga. NSAIDs reduce blood flow to the kidneys, and long-term use can cause direct kidney damage. Farxiga already changes how your kidneys handle fluid and sodium, so the combination puts added stress on kidney function.
The risk is highest if you already have reduced kidney function, are dehydrated, are older, or take diuretics or blood pressure medications at the same time. Occasional use of an NSAID for a headache is a different situation than daily use for arthritis, but it’s worth discussing alternatives with your doctor if you rely on these pain relievers regularly.
Lithium
If you take lithium for bipolar disorder, starting Farxiga can lower your lithium levels. Lithium is chemically similar to sodium, and because Farxiga increases sodium excretion through the kidneys, lithium gets flushed out along with it. Lower lithium levels mean the medication may stop working as well to control mood symptoms.
This interaction is manageable with monitoring. New Zealand’s medicines safety authority recommends checking lithium blood levels more frequently when starting or adjusting Farxiga, and your lithium dose may need to be increased to maintain therapeutic levels.
Alcohol and Ketoacidosis Risk
Alcohol isn’t a drug interaction in the traditional sense, but it deserves attention. Farxiga increases your body’s tendency to produce ketones, the acidic byproducts of fat metabolism. Normally this is mild and harmless. But certain triggers can tip the balance into euglycemic diabetic ketoacidosis, a dangerous metabolic emergency where ketone levels spike even though blood sugar looks normal or only slightly elevated.
Known triggers include heavy alcohol use, prolonged fasting, very low-carb diets, surgery, serious infections, persistent vomiting, and significant dehydration. Alcohol is particularly risky because it independently suppresses glucose production and can mask early warning signs. If you drink, keep it moderate, and be aware that nausea, vomiting, abdominal pain, or unusual fatigue while on Farxiga could signal ketoacidosis rather than a hangover.
Herbal Supplements
There is very little data on how herbal remedies and dietary supplements interact with Farxiga. Unlike prescription drugs, supplements aren’t tested for interactions with other medications in any standardized way. The NHS notes this gap explicitly. If you take herbal products, especially those marketed for blood sugar or blood pressure support, mention them to your pharmacist. Some herbal supplements can lower blood sugar on their own, which could compound Farxiga’s effects.
Before Surgery: When to Stop Farxiga
Farxiga should be stopped at least 3 days before any major surgery or procedure that involves prolonged fasting. The combination of not eating and the drug’s ketone-boosting effect creates a setup for ketoacidosis. You can restart once you’re eating normally again and are clinically stable. If you have a procedure scheduled, make sure your surgical team knows you take Farxiga so they can plan the timing.
Who Should Not Take Farxiga at All
A few situations rule out Farxiga entirely. Anyone who has had a serious allergic reaction to it, such as anaphylaxis or significant swelling, should never take it again. Beyond that, Farxiga is not recommended for people with type 1 diabetes because of the elevated ketoacidosis risk, or for people with polycystic kidney disease or those on immunosuppressive therapy for kidney disease, where the drug simply isn’t expected to work.
Kidney function also determines whether you can start the medication. Farxiga is not recommended for improving blood sugar control if your estimated kidney filtration rate (eGFR) is below 45, because its sugar-lowering mechanism depends on kidney function. For its heart failure and kidney-protective benefits, the cutoff for starting is an eGFR below 25, though people already taking it can continue even below that threshold.