Buy Lasix (Furosemide) — Online Prescription
Furosemide, sold as Lasix, is the most widely used "water pill": a prescription loop diuretic for fluid buildup from heart failure, kidney disease and cirrhosis. This page covers the side effects to watch for, the label dosage chart, how it converts to Bumex and torsemide, what to take it with (and not), and what it costs.
Medically reviewed Medically reviewed by Darcey Melnyk, Pharmacist — NPI 1740713718 · Last updated 2026-10-23
| Active ingredient | Furosemide |
|---|---|
| Dosage form | Tablet (20, 40, 80 mg), oral solution, injection, subcutaneous on-body infusor |
| Administration route | Oral, intravenous, intramuscular, subcutaneous |
Class: Loop Diuretic [EPC]
Indications: INDICATIONS AND USAGE Edema Furosemide tablets are indicated in adults and pediatric patients for the treatment of edema associated with congestive heart failure, cirrhosis of the liver, and renal disease, including the nephrotic syndrome. Furosemide tablets are particularly useful when an agent with greater diuretic potential is desired. Hypertension Oral furosemide may be used in adults for the treatment of hypertension alone or in combination with other antihypertensive agents. Hypertensive p…
Contraindications: CONTRAINDICATIONS Furosemide tablets are contraindicated in patients with anuria and in patients with a history of hypersensitivity to furosemide.
openFDA label data — Updated 2026-10-01Lasix (generic name furosemide) is a prescription "water pill", a loop diuretic that clears fluid buildup from heart failure, kidney disease and cirrhosis, and is sometimes used for blood pressure. Tablets start working within an hour and last 6 to 8 hours. The side effects to watch are dizziness on standing, low potassium (cramps, weakness, irregular heartbeat), dehydration and, rarely, hearing changes. Generic furosemide costs pharmacies about 3 cents a tablet, so price is rarely the obstacle; a prescription and regular bloodwork are.
What Lasix treats and how it works
FDA-approved uses:
- Edema (fluid buildup) from congestive heart failure, cirrhosis of the liver, and kidney disease including nephrotic syndrome, in adults and children. The label notes it is "particularly useful" when a stronger diuretic is needed.
- High blood pressure (oral forms, adults), alone or with other medicines such as an ARB like losartan. It isn't a first choice: patients not controlled on a thiazide usually won't be controlled on furosemide alone.
Lasix and furosemide are the same medicine. Lasix is the original brand; generic furosemide tablets have the same active ingredient at the same 20, 40 and 80 mg strengths, and they're what almost every pharmacy dispenses.
Lasix dosage chart
From the Lasix prescribing information. Doses are set by your prescriber and adjusted to your weight, swelling and bloodwork. This chart is for understanding your prescription, not for changing it.
| Use | Usual starting dose | How it's adjusted | Label ceiling |
|---|---|---|---|
| Edema, adults | 20–80 mg as a single dose | Repeat the same dose, or raise it by 20–40 mg, no sooner than 6–8 hours after the last one. The working dose is then given once or twice a day. | Up to 600 mg a day, only for severe edema with close monitoring |
| High blood pressure, adults | 80 mg a day, usually 40 mg twice a day | Adjusted to response; other blood pressure drugs are often cut by at least half when furosemide is added | Add another medicine rather than climbing |
| Older adults | Low end of the range | Kidneys clear it more slowly, so the first effect is weaker and side effects come easier | Same as adults, more cautiously |
| Children (edema) | 2 mg/kg as a single dose | Up by 1–2 mg/kg, no sooner than 6–8 hours later | 6 mg/kg |
The label also describes an intermittent schedule: for some people, fluid is moved "most efficiently and safely" by taking furosemide on 2 to 4 consecutive days each week rather than daily. If your prescription says something like "Mon–Thu," that's why.
| Form | Strengths | What it looks like / notes |
|---|---|---|
| Tablet | 20 mg, 40 mg, 80 mg | Brand Lasix: white; 20 mg oval marked "Lasix," 40 mg round scored "Lasix 40," 80 mg round scored "Lasix 80." Generics vary in markings. Keep in the light-resistant bottle; don't use discolored tablets. |
| Oral solution | 10 mg/mL, 40 mg per 5 mL | For children or trouble swallowing; absorbed a little faster than tablets |
| Injection (IV/IM) | 10 mg/mL | Hospital or clinic use; works within minutes |
| Subcutaneous infusor | 80 mg dose (Furoscix, Lasix ONYU) | Worn on the belly at home for heart-failure congestion; see below |
How fast it works and when to take it
Starts working. Expect to urinate more, soon.
Peak effect. The heaviest urination is in this window.
Wears off. The half-life is about 2 hours, and tablets deliver about 64% of what the same IV dose does.
- Take it in the morning. If you're on twice a day, take the second dose by early afternoon. The label's own example is 8 am and 2 pm. A late dose means a night of bathroom trips.
- Plan around it. Many people time the dose so they're home for the next 2–3 hours.
- Weigh yourself daily if you have heart failure: same time, same scale. Ask your prescriber how much of a gain should prompt a call, since that's often the first sign your dose needs adjusting.
- Stand up slowly. The label says the dizziness on standing that sometimes occurs "can usually be managed by getting up slowly."
Lasix side effects
The label lists side effects by body system without percentages. Most are extensions of what the drug does: it removes fluid and salts, sometimes more than you need.
From the fluid loss itself
- Urinating often, especially 1–2 hours after a dose
- Thirst and dry mouth
- Lightheadedness when you stand up
- Mild nausea, diarrhea or constipation
- Sunburning more easily
Signs something is off
- Muscle cramps, weakness, unusual tiredness (low potassium or magnesium)
- Confusion, drowsiness or restlessness (low sodium, dehydration)
- Ringing in the ears or muffled hearing
- A painful, swollen joint (gout: furosemide raises uric acid)
- Higher blood sugar readings if you have diabetes
- Much less urine than usual, or trouble emptying your bladder
Rare but serious
- Fainting, or a racing or irregular heartbeat
- Blistering, peeling rash or sores in the mouth
- Swelling of the face, lips or throat, trouble breathing
- Yellow skin or eyes, or severe stomach pain
- Producing little or no urine at all
In older adults the label adds a specific caution: too much fluid loss can cause dehydration and a drop in blood volume severe enough to cause collapse or blood clots, "particularly in elderly patients." Falls from dizziness on standing are the everyday version of that risk. Starting low and keeping regular blood tests is the label's answer.
Sulfa allergy: furosemide is a sulfonamide, and the label says people allergic to sulfonamides may also react to it. Tell your prescriber and pharmacist if you've had a sulfa reaction.
Potassium and bloodwork
Furosemide makes your kidneys excrete potassium along with sodium and water. The label calls for checking electrolytes (especially potassium), kidney function and CO2 frequently during the first few months and periodically after that. Low potassium is more likely with brisk fluid loss, a poor diet, cirrhosis, or steroids, large amounts of licorice or long-term laxatives. With digoxin, low potassium is especially dangerous for heart rhythm.
Many people on furosemide are also prescribed a potassium supplement, a potassium-sparing medicine (such as spironolactone) or diet changes. If you vomit a lot or have diarrhea for more than a day, call your prescriber: that's when electrolytes drop fastest. Furosemide is contraindicated if you can't make urine (anuria).
Drug interactions
From the Lasix label. Tell your pharmacist about every prescription, OTC drug and supplement you take.
| Taken with | What can happen |
|---|---|
| Aminoglycoside antibiotics (gentamicin, tobramycin), cisplatin, ethacrynic acid | Higher risk of hearing damage. Avoided except in life-threatening situations. |
| Lithium | Lithium builds up to toxic levels. Generally not combined. |
| ACE inhibitors and ARBs (lisinopril, losartan) | Blood pressure can fall sharply and kidney function can worsen. Doses are often adjusted. |
| NSAIDs (ibuprofen, naproxen, indomethacin) | Can blunt the diuretic and blood-pressure effect and strain the kidneys |
| Digoxin | Low potassium from furosemide raises the risk of digoxin heart-rhythm effects |
| Sucralfate | Lowers furosemide's effect. Take them at least 2 hours apart. |
| High-dose aspirin | Salicylate toxicity at lower doses than usual |
| Steroids, large amounts of licorice, long-term laxatives | Add to potassium loss |
| Phenytoin | Less furosemide absorbed, weaker effect |
| Cyclosporine | Higher risk of gout |
| Alcohol, sleeping pills, opioid pain medicines | Worse dizziness and blood-pressure drop on standing |
| OTC decongestants and diet pills | Can raise blood pressure. The label tells people with hypertension to avoid them. |
Lasix vs. Bumex vs. torsemide (and conversion)
All three are loop diuretics that work the same way. They differ in strength per milligram, how reliably they're absorbed, and how long they last. Here is what each FDA label says:
| Furosemide (Lasix) | Bumetanide (Bumex) | Torsemide (Demadex, Soaanz) | |
|---|---|---|---|
| Equivalence to furosemide (label) | Reference | 1 mg ≈ 40 mg furosemide | No conversion ratio on the label |
| Usual starting dose for edema | 20–80 mg | 0.5–2 mg a day | 10–20 mg once a day (heart failure) |
| Label ceiling | 600 mg a day (severe edema) | 10 mg a day | Doses above 200 mg not studied |
| Oral absorption | About 64% of an IV dose, variable between people | Rapid onset, short action | Once-daily dosing |
| If you're allergic to furosemide | Contraindicated | Cross-sensitivity rarely seen; the label notes it has been used successfully | Ask your prescriber |
| Generic | Yes | Yes | Yes |
So, on the labels, 40 mg of furosemide corresponds to about 1 mg of bumetanide. Torsemide has no labeled ratio, and prescribers set its dose individually. Is one better? In TRANSFORM-HF, the largest head-to-head trial (2,859 patients hospitalized with heart failure, JAMA 2023), deaths were essentially identical: 26.1% on torsemide vs. 26.2% on furosemide. A switch usually happens because furosemide's variable absorption isn't controlling someone's fluid, not because the other drug is generally superior.
Furosemide at home under the skin: Furoscix and Lasix ONYU
Two newer brands deliver furosemide subcutaneously (under the skin of the belly) with a wearable on-body infusor, so some people with heart-failure congestion can be treated at home instead of getting IV furosemide in a hospital.
Furoscix
- Approved for
- Edema in adults with chronic heart failure or chronic kidney disease (and children 43 kg and up)
- How it's given
- 80 mg: on-body infusor over 5 hours, or a ReadyFlow device in about 10 seconds
- Use
- Short-term, then back to tablets as soon as practical
Lasix ONYU
- Approved for
- Edema in adults with chronic heart failure
- How it's given
- On-body infusor: 30 mg in the first hour, then 12.5 mg an hour for 4 hours
- Use
- Short-term, then back to tablets as soon as practical
Both are brand-only and cost far more than tablets, so insurers often require prior authorization. Call us to check stock and coverage before your prescription is sent.
Lasix price and how to buy
Generic furosemide is one of the cheapest prescriptions in the US. CMS's NADAC survey of October 21, 2026 shows what pharmacies pay:
Source: CMS National Average Drug Acquisition Cost (data.medicaid.gov), per-tablet prices × 30. Brand Lasix costs pharmacies about 36 times as much as generic at 40 mg. Retail cash prices are higher than these costs; see the price table on this page.
- Ask for the cash price. For generic furosemide, the pharmacy's cash price is often lower than an insurance copay.
- Any prescriber can write it. A primary care visit, urgent care or a telehealth visit can prescribe furosemide when it's appropriate, and order the follow-up bloodwork.
- We fill it fast. Have your prescriber send it to Arrow Pharmacy, or call (860) 522-9289 to transfer an existing prescription. We deliver free in the Hartford area.
A website that sells furosemide with no prescription is skipping the bloodwork that keeps it safe, and is usually an unlicensed pharmacy. See our guide to checking an online pharmacy before ordering anything online.
Shortage reported — Affects: Furosemide, Injection, 10 mg/1 mL (NDC 63323-280-02). If that's not the form or strength you take, ask your pharmacist whether your specific product is affected.
FDA openFDA — Updated 2026-11-01National Average Drug Acquisition Cost (NADAC): $0.029 per tablet (FUROSEMIDE 40 MG TABLET). This is the average price pharmacies pay wholesalers — not your out-of-pocket cost — published by CMS for pricing transparency.
CMS NADAC — Updated 2026-11-01Lasix (Furosemide) Prices in the USA
| Dosage | Brand-name avg. price | Generic avg. price |
|---|---|---|
| 20 mg | $40–70 / 30 tablets | $8–15 / 30 tablets |
| 40 mg | $45–90 / 30 tablets | $8–18 / 30 tablets |
| 80 mg | $60–110 / 30 tablets | $12–25 / 30 tablets |
Frequently asked questions
Can I buy Lasix (furosemide) over the counter in the US?
No. Furosemide is prescription-only in the United States in every form: tablets, oral solution, injection and the subcutaneous infusors. It needs a prescriber because it can drain potassium, sodium and fluid too far, and the label calls for regular bloodwork during the first months. Generic furosemide is cheap, so getting a prescription is usually the only real hurdle.
What are the most common side effects of Lasix?
Needing to urinate often (that is how it works), dizziness when standing up, thirst and dry mouth, muscle cramps and weakness from low potassium, and sometimes nausea or diarrhea. The ones to call your prescriber about are signs of low potassium or sodium (weakness, cramps, an irregular heartbeat, confusion), ringing in the ears or hearing changes, a gout flare, or passing much less urine than usual.
What is the generic name for Lasix?
Furosemide. Lasix is the original brand, and nearly every prescription today is filled with generic furosemide tablets, which are the same drug at the same strengths (20, 40 and 80 mg). Furoscix and Lasix ONYU are newer brands of furosemide given under the skin with a wearable infusor for heart-failure fluid buildup at home.
What is the maximum dose of Lasix in 24 hours?
The label allows a carefully titrated maximum of 600 mg a day, but only for severe fluid overload under close monitoring. Typical adult doses are far lower: 20 to 80 mg as a single dose for edema, repeated or raised by 20 to 40 mg no sooner than 6 to 8 hours later, and 40 mg twice a day for blood pressure. Never raise your own dose.
How long does it take Lasix to work?
Furosemide tablets start working within an hour, the effect peaks in the first 1 to 2 hours, and it lasts 6 to 8 hours (FDA label). That's why you'll urinate a lot soon after a dose, and why a second daily dose is usually taken by mid-afternoon (the label's example is 8 am and 2 pm) so you're not up all night.
What is the Bumex to Lasix conversion?
The bumetanide (Bumex) label says 1 mg of bumetanide has about the same diuretic effect as 40 mg of furosemide, a 1:40 ratio. Torsemide's label gives no conversion ratio; its usual starting dose for heart-failure edema is 10 to 20 mg once a day. Switching between loop diuretics is done by your prescriber, usually followed by a check of your weight, fluid and potassium.
Why does Lasix lower potassium?
Furosemide makes your kidneys excrete potassium along with sodium and water. Low potassium can cause cramps, weakness and dangerous heart rhythms, especially if you also take digoxin. The label calls for checking electrolytes frequently in the first few months. Many people are prescribed a potassium supplement, a potassium-sparing drug, or diet changes alongside it.
Is Lasix safe for elderly patients?
Yes, with more caution. The label advises starting at the low end of the dose range in older adults, whose kidneys clear furosemide more slowly. The main risks are dehydration, dizziness and falls from a drop in blood pressure on standing, and low potassium or sodium. Getting up slowly, keeping regular blood tests and reporting confusion or unusual weakness all help.
Can I take Lasix if I am allergic to sulfa drugs?
Tell your prescriber and pharmacist first. Furosemide is a sulfonamide, and its label says people allergic to sulfonamides may also be allergic to it. Many people with a sulfa-antibiotic allergy take furosemide without trouble, but the decision should be made with your prescriber, who may choose another diuretic if your reaction was severe.
Does Lasix lower blood pressure?
It can, and oral furosemide is FDA-approved for high blood pressure, usually 40 mg twice a day. But it is rarely a first choice for routine hypertension: the label notes that patients not controlled on a thiazide probably won't be controlled on furosemide alone. Its main job is clearing fluid from heart failure, kidney disease and cirrhosis.
Sources
- LASIX (furosemide) tablets — FDA-approved prescribing information — U.S. National Library of Medicine (DailyMed) / Validus Pharmaceuticals
- Bumetanide tablets — FDA-approved prescribing information (1 mg bumetanide ≈ 40 mg furosemide) — U.S. National Library of Medicine (DailyMed)
- Torsemide tablets — FDA-approved prescribing information — U.S. National Library of Medicine (DailyMed)
- FUROSCIX (furosemide) subcutaneous injection — prescribing information — U.S. National Library of Medicine (DailyMed) / scPharmaceuticals
- LASIX ONYU (furosemide) subcutaneous injection — prescribing information — U.S. National Library of Medicine (DailyMed) / SQ Innovation
- Effect of Torsemide vs Furosemide After Discharge on All-Cause Mortality in Patients Hospitalized With Heart Failure: The TRANSFORM-HF Randomized Clinical Trial (JAMA, 2023) — PubMed / JAMA
- NADAC (National Average Drug Acquisition Cost) — furosemide and LASIX tablets, survey of October 21, 2026 — CMS
- openFDA Drug Shortages — U.S. FDA
- Furosemide / Lasix price data (average retail cash price) — GoodRx (consumer price reference)