Leucovorin Side Effects: What to Expect and When to Call Your Doctor

What You Should Know About Leucovorin Side Effects

If your doctor has prescribed Leucovorin (also known as Folinic Acid or by the brand name Wellcovorin), you're probably wondering what side effects to expect. The answer depends largely on why you're taking it and what other medications you're using alongside it.

Leucovorin on its own is generally well tolerated. But when it's combined with chemotherapy drugs like 5-Fluorouracil (5-FU) — which is the most common clinical scenario — the side effect profile changes significantly. This guide covers both situations so you know exactly what to watch for.

What Is Leucovorin?

Leucovorin Calcium is a reduced form of Folic Acid. It's used in three main ways: as a "rescue" agent after high-dose Methotrexate therapy, as a chemotherapy enhancer with 5-FU for colorectal cancer, and to treat megaloblastic anemia when oral Folic Acid isn't an option. For a deeper look, read our complete guide on what Leucovorin is and how it's used.

Common Side Effects

When used alone (such as for Methotrexate rescue or megaloblastic anemia), Leucovorin's side effects are typically mild. Based on FDA labeling, the most commonly reported side effects include:

• Nausea — A feeling of queasiness, usually mild and temporary
• Vomiting — More common with higher doses or IV administration
• Diarrhea — Can range from mild to moderate
• Stomatitis — Sores or inflammation in the mouth
• Allergic sensitization — Skin rash, hives (urticaria), or itching

These side effects are generally manageable and often resolve on their own. If you experience persistent nausea or diarrhea, your doctor may recommend anti-nausea medication or dietary adjustments.

Side Effects When Combined With 5-Fluorouracil

The picture changes when Leucovorin is used as part of chemotherapy for colorectal cancer. Leucovorin enhances the effects of 5-FU, which means it also amplifies the side effects. When used together, patients may experience:

• Severe diarrhea — Can become life-threatening if not managed promptly. Report any diarrhea lasting more than 24 hours.
• Severe stomatitis and mouth sores — Painful sores that can make eating and drinking difficult
• Myelosuppression — Low white blood cell counts (increasing infection risk), low red blood cells (anemia), and low platelets (increasing bleeding risk)
• Nausea and vomiting — More severe than with Leucovorin alone
• Fatigue and weakness — Related to the overall chemotherapy effect

These combination-related side effects are serious and require close monitoring by your oncology team. Your doctor will order regular blood tests to check your cell counts throughout treatment.

Serious Side Effects — When to Call Your Doctor Immediately

While rare, some side effects require immediate medical attention. Call your doctor or go to the emergency room if you experience:

• Signs of a severe allergic reaction — Difficulty breathing, swelling of the face or throat, severe hives, or feeling like you might pass out
• Anaphylactoid reactions — These can occur with both oral and injectable Leucovorin and require emergency treatment
• Seizures — Reported in patients receiving Leucovorin with high-dose Methotrexate, particularly in those with a history of seizure disorders
• Severe, uncontrollable diarrhea — Especially when taking Leucovorin with 5-FU. Dehydration from severe diarrhea can be fatal if untreated.
• Signs of infection — Fever over 100.4°F, chills, sore throat, or body aches (may indicate myelosuppression)
• Unusual bleeding or bruising — Nosebleeds, bleeding gums, blood in urine or stool

Important safety note: Leucovorin must never be given intrathecally (into the spinal canal). This can be fatal. It should only be given orally, by IV, or by intramuscular injection.

Specific Populations at Higher Risk

Pregnant and Nursing Women

Leucovorin is classified as Pregnancy Category C under the prior FDA system. It has not been adequately studied in pregnant women. If you are pregnant or planning to become pregnant, discuss the risks and benefits with your doctor. It is also unknown whether Leucovorin passes into breast milk, so nursing mothers should use caution.

Children

Leucovorin is used in pediatric patients, particularly for Methotrexate rescue in osteosarcoma treatment. Dosing is based on body surface area. Side effects in children are similar to those in adults.

Elderly Patients

Older adults may be more sensitive to the GI side effects of Leucovorin, especially when combined with 5-FU. Kidney function often declines with age, and since impaired renal function can delay Methotrexate clearance, elderly patients may need adjusted Leucovorin dosing.

Patients With Kidney Problems

If your kidneys aren't working well, Methotrexate can build up in your body to dangerous levels. In these cases, your doctor may increase your Leucovorin dose or extend the duration of rescue therapy. Regular lab monitoring is essential.

How to Manage Leucovorin Side Effects

Here are practical tips to help you manage the most common side effects:

For Nausea and Vomiting

• Eat small, frequent meals instead of large ones
• Avoid greasy, spicy, or strong-smelling foods
• Ask your doctor about anti-nausea medications like Ondansetron (Zofran)
• Stay hydrated — sip water, clear broth, or electrolyte drinks throughout the day

For Diarrhea

• Drink plenty of fluids to prevent dehydration
• Follow a bland diet (bananas, rice, applesauce, toast)
• Ask your doctor before taking over-the-counter anti-diarrheal medications
• Report diarrhea lasting more than 24 hours or more than 4-6 loose stools per day

For Mouth Sores

• Use a soft toothbrush and gentle mouthwash (avoid alcohol-based products)
• Rinse with a baking soda and salt water solution several times a day
• Avoid hot, acidic, or rough-textured foods
• Your doctor may prescribe a special mouth rinse if sores are severe

For Allergic Reactions

• Tell your doctor about any previous allergies to Folic Acid or Leucovorin before starting treatment
• Mild rashes may be managed with antihistamines
• Seek immediate help for any breathing difficulty or severe swelling

Final Thoughts

Leucovorin's side effects range from mild (nausea, rash) when used alone to potentially serious (severe diarrhea, myelosuppression) when combined with chemotherapy drugs like 5-FU. The key is knowing what to expect, staying in close contact with your medical team, and reporting any concerning symptoms right away.

If you're having trouble finding Leucovorin at your pharmacy, Medfinder can help you locate it in stock near you. And for more information about this medication, check out our guides on how Leucovorin works and drug interactions to watch for.