How long does Zofran take to work?

In this article:

• How long does Zofran take to work? 
• What can affect how long it takes Zofran to work?
• What is the standard Zofran dosage?
• Zofran vs. ondansetron
• Who should avoid taking Zofran?
• The bottom line

In this article

• How long does Zofran take to work? 
• What can affect how long it takes Zofran to work?
• What is the standard Zofran dosage?
• Zofran vs. ondansetron
• Who should avoid taking Zofran?
• The bottom line

Are you feeling queasy? Nausea and vomiting are uncomfortable but common symptoms that can be caused by illness, gastrointestinal issues, cancer treatments, medication side effects, anesthesia, and pregnancy. When over-the-counter (OTC) remedies don’t cut it, your healthcare provider may prescribe Zofran (ondansetron), a medication used to treat upset stomach and prevent vomiting—especially when caused by chemotherapy, radiation therapy, and surgery. It’s also can be used off-label to treat morning sickness during pregnancy.

Zofran belongs to a class of drugs called antiemetics, which work by blocking certain chemical receptors in the body that can trigger nausea. Though the brand name Zofran is no longer available, the generic is still widely used. It provides quick relief, alleviating nausea and vomiting in about 30 minutes. Zofran’s exact onset of action may vary depending on factors such as the dosage administered and various patient-specific factors.

How long does Zofran take to work? 

Zofran typically begins to work within 30 minutes to two hours, says Sazan Sylejmani, Pharm.D., owner and pharmacy manager at Westmont Pharmacy in Illinois. Within that time frame, you can expect a significant reduction in nausea and vomiting.

The dosage form impacts how long Zofran takes to kick in. “For instance, the orally disintegrating tablet (ODT) might act faster due to its sublingual absorption, while the oral tablet might take a bit longer as it has to pass through the digestive system,” says Dr. Sylejmani.

“Zofran ODT or ondansetron ODT has a rapid onset of action, with its peak antiemetic effect within 15-30 minutes,” explains Robert Glatter, MD, a board-certified emergency medicine physician at Lenox Hill Hospital in New York. Higher doses of Zofran may work more efficiently to relieve and prevent nausea and vomiting in the same time frame.

What can affect how long it takes Zofran to work?

The following factors can impact how quickly Zofran works.

• Metabolic rate:  Dr. Glatter explains that specific enzymes in the liver that break down Zofran to its active metabolites may impact how efficiently it works to prevent nausea and vomiting. 
• Age: Dr. Sylejmani says older adults may experience a delayed onset. That’s because the liver slows down with age, causing medications to be metabolized more slowly.
• Other medications: Dr. Sylejmani says some medicines can interact with Zofran and affect its absorption or effectiveness. To avoid potential complications, it’s essential to inform your healthcare provider about any other medications you are taking.
• Dosage and formulation: Higher doses and the intravenous (IV) formulation of ondansetron lead to faster onset and more efficient relief of nausea and vomiting symptoms, says Dr. Glatter. For Zofran to kick in as fast as possible, the sublingual option is typically your best bet (unless you’re in a hospital setting where an IV is being used), says Dr. Sylejmani.

What is the standard Zofran dosage?

“The usual dosage for adults is 8 mg administered two to three times daily,” says Dr. Sylejmani. However, it can vary based on the type of nausea being treated. “For instance, preventing postoperative nausea usually requires a single 16 mg dose before surgery, whereas chemotherapy-induced nausea might need repetitive doses,” he explains.

Dosage recommendations for Zofran vary depending on the intended treatment.

Zofran dosage guidelines
Indication	Adult dosage	Children 12 to 17 dosage	Children 4 to 11 dosage
Moderate nausea and vomiting from chemotherapy	8 mg taken 30 minutes before chemotherapy, a second 8 mg dose 8 hours after the first dose, and an 8 mg dose every 12 hours for 1 to 2 days after chemotherapy.	8 mg taken 30 minutes before chemotherapy, a second 8 mg dose 4 and 8 hours after the first dose, and an 8 mg dose 3 times a day for 1 to 2 days after chemotherapy.	4 mg taken 30 minutes before chemotherapy, a second 4 mg dose taken 4 and 8 hours after the first dose, and a 4 mg dose taken three times daily for 1 to 2 days after chemotherapy.
Severe nausea and vomiting from chemotherapy	24 mg taken 30 minutes before starting cancer treatment.	Consult a healthcare professional.	Consult a healthcare professional.
Nausea and vomiting from radiotherapy	8 mg taken 1 to 2 hours before each fraction of radiotherapy daily.	Consult a healthcare professional.	Consult a healthcare professional.
Post-surgical nausea and vomiting	16 mg taken 1 hour before anesthesia.	Consult a healthcare professional.	Consult a healthcare professional.

Zofran vs. ondansetron

The FDA withdrew Zofran oral dissolving tablets (ODT) from the market in 2023, but not due to safety or effectiveness; instead, the decision was related to packaging concerns, says Dr. Glatter. “The use of hospital-type packaging (blister packs) that could place pediatric patients at risk for overdose (if they swallowed the pills) was the overriding concern.” The blister packs did not adhere to federal packaging requirements.

Though other versions of Zofran weren’t recalled, Dr. Glatter says they are no longer available—primarily due to patent expiration. “The cost of the medication is the main driver behind the lack of availability at big box pharmacies. This involves a cost to patients as well as the cost to the pharmacy of procuring brand-name Zofran products,” he explains.

While the brand name has been discontinued, the generic versions of Zofran and Zofran ODT—ondansetron and ondansetron ODT—are still available to consumers, and they’re chemically identical.

 “Ondansetron has the same active pharmaceutical ingredient as Zofran, but other ‘fillers’ may be added to ensure the stability of the medication,” says Dr. Glatter. Fillers are safe to add to generic versions of medications and do not impact their effectiveness. In other words, whether you take ondansetron or Zofran, they are equally effective.

Who should avoid taking Zofran?

Zofran is an effective anti-nausea medication, but certain people should use it cautiously or avoid it. Patients with the following medical conditions should consult their healthcare provider before using Zofran:

• Individuals with heart disease, a heart rhythm issue, or a history of an irregular heartbeat (such as patients with congenital long QT syndrome)
• Individuals with liver disease or impairment
• Individuals who have had an allergic reaction to ondansetron or other serotonin 5-HT3 receptor antagonist medications 

For pregnant patients, the American College of Gynecology, recommends avoiding use before the first trimester. However, the use of ondansetron may be considered for the treatment of severe or refractory nausea and vomiting when preferred agents have failed. 

Due to the possibility of Zofran interacting with other common medications, you should speak with your health care provider prior to starting any new medications while taking Zofran as patient-specific factors play a role in how a drug interaction may affect you. 

The bottom line

Zofran acts fast to relieve nausea and vomiting. In most cases, it takes 30 minutes to work, but the time varies from 15 minutes to two hours based on factors like liver metabolism, patient age, dosage formulation, and concurrent medications. For best results, take Zofran as your healthcare provider prescribes and discuss your current medications, dietary supplements, and health conditions to avoid adverse interactions.