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Buy Ondansetron 4Mg and 8Mg Tablets from Canada Online



Ondansetron is an FDA-approved medication used to prevent vomiting & nausea caused by radiation therapy, cancer chemotherapy, and surgery. This medicine is in a group of drugs known as serotonin 5-HT3 receptor antagonists. It helps by stopping the effects of serotonin, a natural substance that can cause nausea & vomiting. Ondansetron can be taken orally and available in two strengths: 4 mg & 8 mg. So, if you want to buy Ondansetron online from a Canadian Pharmacy, you need to get a prescription from your doctor.

Product Overview

Ondansetron is a medicine approved by the FDA to stop vomiting and nausea caused by treatments like radiation, chemotherapy, and surgery. It falls under a group called serotonin 5-HT3 receptor antagonists and works by blocking the effects of serotonin, a natural substance that makes you feel nauseous. This drug comes in two strengths, 4 mg, and 8 mg, and you’ll need a prescription from your doctor to buy it online from a Canadian Pharmacy.

For adults going through chemotherapy, a single 24-mg dose is recommended 30 minutes before the session for high nausea likelihood, while an 8 mg dose is advised for moderate cases, with additional doses later. Kids and older adults may need different amounts based on their age. Ondansetron is available in various forms, such as tablets and solutions.

To take Ondansetron, you can have it with or without food, following your doctor’s instructions carefully. It works by stopping a chemical in the brain called serotonin, preventing nausea and vomiting after cancer treatment or surgery. Common side effects include headaches and tiredness, while serious ones like chest pain need immediate medical help.

Remember to store Ondansetron in a place that’s not too hot or cold and away from light or wet areas. If you miss a dose, take it as soon as you remember, or skip it if it’s close to the next one. In case of overdose symptoms, seek medical help right away. If you have any questions or experience allergies, talk to your doctor for guidance and management.

Uses of Ondansetron

  • Prevention of vomiting & nausea associated with HEC or MEC
  • Prevention of vomiting & nausea associated with first and follow-up rounds of emetogenic chemotherapy

How to Use Ondansetron?


Ondansetron can be taken orally and available in 4 forms such as orally disintegrating tablet, regular tablets, film, and solution. It is available in 2 strengths as follows:

  • 4 mg
  • 8 mg

Recommended Dosage for Different Age Groups

  • Adults (18–64 years): For chemotherapy highly likely to induce nausea and vomiting, a single 24-mg dose is recommended 30 minutes before the session. For moderately likely nausea and vomiting, an 8 mg dose is advised 30 minutes before chemotherapy. An additional 8 mg can be taken eight hours later, followed by 8 mg twice per day for 1–2 days post-chemotherapy.
  • Children (12–17 years): For chemotherapy moderately likely to cause nausea and vomiting, a dosage of 8 mg is recommended 30 minutes before treatment. Additional 8 mg doses can be administered four and eight hours after the initial dose. Post-chemotherapy, 8 mg can be taken three times per day for 1–2 days.
  • Children (4–11 years): For chemotherapy moderately likely to induce nausea and vomiting, a 4 mg dose is recommended 30 minutes before chemotherapy. Additional 4 mg doses can be taken four and eight hours later. Post-chemotherapy, a 4 mg dose can be taken three times per day for 1–2 days.
  • Children (0–3 years): Ondansetron’s safety and effectiveness in children under 4 years have not been confirmed. It is not recommended for use in this age group.
  • Seniors (65 years and older): Due to potential decreases in kidney function in older adults, drug processing may be slower. This can result in a higher drug concentration in the body, increasing the risk of side effects. Adjustments in dosage may be necessary for this age group.

If you have serious liver disease, don’t take more than 8 mg of Ondansetron in a day.

[Note: Remember these recommendations may vary depending on person to person. Discuss it with your doctor, and they’ll customize your dosage accordingly.]

How to Take It?

  • You can take Ondansetron with or without food.
  • The first dose is usually before your surgery, chemotherapy, or radiation treatment. Follow your doctor’s instructions carefully.
  • For the regular tablet, take it with a full glass of water.
  • If you have the orally disintegrating tablet, keep it in the blister pack until you’re ready to take it. Open the pack and peel back the foil. Don’t push it through the foil.
  • Use dry hands to take the tablet and put it in your mouth.
  • Let this medication dissolve in your mouth without chewing.
  • Swallow a few times as it dissolves.
  • If you’re using ondansetron oral soluble film, keep the strip in the foil pouch until you’re ready to use it.
  • With dry hands, take the strip and put it on your tongue. It will start to dissolve right away.
  • Let it dissolve in your mouth without chewing.
  • Swallow a few times after the strip dissolves. If you want, you can drink something to help swallow the dissolved strip.
  • If you are taking liquid form, measure liquid medicine with a medicine cup or dose-measuring spoon. If you don’t have a measuring device, ask your pharmacist for one.

[Note: Your doctor will decide the right amount for you based on your condition, following guidelines and studies on the drug. They’ll adjust it as needed over time.]

How Does Ondansetron Work?

Ondansetron, a medication designed to prevent nausea and vomiting, achieves its effect by inhibiting the action of serotonin, a messenger chemical in the brain. This mechanism is particularly beneficial for individuals experiencing nausea as a side effect of cancer treatment (chemotherapy) or surgery. The hypothesis suggests that Ondansetron functions by blocking two specific sites: centrally, in the area postrema/NTS, and peripherally, on vagus nerve terminals. This dual-action approach contributes to its efficacy in managing and alleviating nausea associated with various medical interventions.

Important Safety Information

Side Effects

Common side effects of Ondansetron include:

  • Headache
  • Tiredness
  • Weakness
  • Chills
  • Drowsiness
  • Constipation

Serious side effects of Ondansetron include:

  • Chest pain
  • Fainting, dizziness, or light-headedness
  • Difficulty breathing or swallowing
  • Rash, hives, or itching
  • Fast, slow, or irregular heartbeat
  • Swelling of the eyes, lips, face, tongue, hands, throat, ankles, feet, or lower legs
  • Blurred vision or vision loss
  • Hallucinations 
  • Fever
  • Excessive sweating
  • Confusion
  • Nausea, vomiting, or diarrhea
  • Loss of coordination
  • Stiff or twitching muscles
  • Seizures
  • Coma (loss of consciousness)
  • Agitation

[Note: Remember, this list may not cover all possible side effects. Always consult with your healthcare giver for medical advice about side effects.]


For People with Risk Factors for Heart Arrhythmias: If you have factors that make you more likely to have heart rhythm problems, like heart failure or congenital long QT syndrome, using this medication may raise the chance of arrhythmias for you. It’s essential to discuss with your doctor if you have any risks for arrhythmias.

For People with Phenylketonuria: If you have phenylketonuria, it’s important to note that the orally disintegrating tablet of ondansetron contains phenylalanine. This amino acid can be harmful to individuals with phenylketonuria. Therefore, if you have phenylketonuria, avoid taking the orally disintegrating tablet. Always consult your doctor for the most suitable options for your condition.

People with Allergies: Be cautious of potential allergies to Ondansetron, as it may trigger a severe allergic reaction with symptoms such as flushing, difficulty breathing, throat or tongue swelling, dizziness, and coughing. It’s crucial not to use this medication if you’ve previously had an allergic reaction to it, as taking it again could be life-threatening and may lead to fatal outcomes.


Pregnant Women: There haven’t been enough studies in people to be sure how ondansetron might affect a baby when a pregnant mom takes it. While research in animals didn’t show harm to the fetus, animal studies may not always predict human reactions. If you’re pregnant or planning to be, talk to your doctor. Only use this drug during pregnancy if it’s absolutely necessary.

Breastfeeding Women: Ondansetron can go into breast milk and may cause severe side effects in a breastfed baby. If you breastfeed, discuss it with your doctor. You might need to decide whether to stop breastfeeding or discontinue this medication.

Seniors: As people get older, their kidneys may not work as well, making the body process drugs more slowly. This can lead to a higher drug level in the body, increasing the risk of side effects. Seniors should use ondansetron cautiously.

Children: This medication hasn’t been studied in children under 4 years old, so it’s not recommended for use in this age group.

Missed Dose

If you forget to take Ondansetron, take it when you remember. If it’s almost time for your next Ondansetron dose, skip the missed one & stick to your regular schedule. You can avoid taking two Ondansetron doses at once. If you miss more than one dose, talk to your healthcare provider. They can guide you on how to get back on track with your usual routine.

[Note: If you have missed a dose of your medication and are unsure about when to take the next one, immediately consult your doctor or pharmacist.]


Ondansetron overdose symptoms may indicate a sudden loss of vision, significant constipation, feelings of light-headedness, or fainting. These signs include a temporary loss of vision, dizziness, fainting, constipation, and an irregular heartbeat. If any of these symptoms occur, it is essential to seek immediate medical assistance for treatment.

[Note: If you consumed more than the recommended dose, get medical help immediately or call the Poison Help line at 1-800-222-1222.]


  • Keep the tablets in a place where the temperature is not too hot or cold, between 36°F & 86°F (2°C and 30°C).
  • Make sure to keep this medicine away from light.
  • Don’t store it in wet or humid places like bathrooms.

[Note: Discuss with your healthcare professional about the proper disposal of any unused medicine and any questions you may have regarding its storage.]

Ondansetron Interactions

Ondansetron has several medication interactions, such as:

  • Apomorphine
  • Drugs affecting heart rhythm 
  • Serotonergic medications
  • Tramadol
  • Carbamazepine
  • Phenytoin and Rifampicin

[Note: This isn’t a complete list, and there could be other drugs that interact with Ondansetron. Make sure to tell your doctor about any prescription, over-the-counter medicines, and herbal products you’re taking.]

Ondansetron Alternatives

  • Phenergan (promethazine)
  • Reglan (metoclopramide)
  • Compro (prochlorperazine)
  • Compazine (prochlorperazine)
  • Dramamine Less Drowsy (meclizine)
  • Lorazepam (ativan)
  • Dimenhydrinate (dramamine)

[Note: Your doctor will choose what’s best for you. Don’t use any of these alternative medications without consulting your healthcare provider. Taking them by yourself may cause serious side effects.] 

Frequently Asked Questions

How long does ondansetron take to work?

The oral form of Ondansetron starts working fast, usually in about 30 minutes, but sometimes it takes up to two hours for the full effect. You take it before getting treatments or procedures that could make you feel sick or lead to vomiting. For example, you usually take it 30 minutes before chemotherapy, an hour before surgery, or 1 to 2 hours before radiation treatments. Your doctor will let you know when to take the medicine, and sometimes, you might need more than one dose to stay comfortable.

When should you take Ondansetron?

You can take Ondansetron with a full glass of water, with or without food. Follow the doctor’s instructions on how much to take and for how long. Normally, you’d take the first dose of Ondansetron before your surgery, chemotherapy, or radiation treatment begins. It’s important to stick to your doctor’s recommendations for the best results. If you have any questions, just ask your doctor.

Is it safe to take Ondansetron by children?

A healthcare professional should guide children when taking Ondansetron. During chemotherapy or after surgery, Ondansetron is often prescribed to treat nausea & vomiting in children. In addition to the child’s weight, the dosage is determined by their medical condition. Always follow your healthcare provider’s recommendations for proper administration and dosage adjustments.

Can I buy Ondansetron over the counter?

It is not possible to purchase Ondansetron over the counter. A prescription is required from a healthcare professional. Ondansetron is commonly prescribed to prevent nausea and vomiting associated with chemotherapy and surgery. Consult your healthcare provider if Ondansetron is necessary for your medical condition and obtain a prescription.

Does Ondansetron cause allergic reactions?

If you use Ondansetron and notice skin irritation, itching, swelling, or strong dizziness, you might be allergic. Get medical help right away if this happens. Let your healthcare provider know about any unusual reactions, especially if you already have allergies, so they can guide you on what to do.

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