Flagyl

Medically Reviewed by Dr. Harshi Dhingra, M.D.

Last Reviewed: Jul 06, 2022

Warnings

What are the risks of taking Flagyl?

Flagyl (metronidazole) can cause serious health problems and adverse reactions, especially in certain high-risk patients. Please talk to your doctor or pharmacist about other treatment options if these are a concern for you.

CANCER RISK: Animal studies indicate that long-term use of Flagyl may be associated with an increased risk of cancer. Talk to your doctor if you have new or worsening symptoms after completing the prescribed treatment course. Do not use Flagyl for longer than prescribed.
SEIZURES: Rarely people taking Flagyl can experience abnormal brain function or seizures. The symptoms may include uncontrolled shaking of the body, trouble speaking, and inability to walk straight. This is a serious side effect, and you should call your doctor or go to the ER right away if you have anything that looks like seizures while taking Flagyl. The risk is higher with bigger doses and long-term treatment
NERVE DAMAGE: In a small number of people, Flagyl (metronidazole) can cause nerve damage, leading to symptoms such as numbness, tingling, burning, pain, and cold/heat intolerance in the hands and feet. Discontinue Flagyl and call your doctor right away if this occurs. The nerve damage can be permanent if not stopped in time. The risk of this occurring is higher with large doses and long-term treatment.
STOMACH INFECTION: Taking Flagyl (metronidazole) for longer than required can affect your gut flora (good bacteria in the gut). As a result, other harmful bacteria can grow out of control, leading to symptoms like diarrhea, bloody stools, and stomach cramps. This usually occurs within a few weeks of taking the last Flagyl dose. Call your doctor immediately if you experience these symptoms because they can indicate more serious infections.

Your doctor or pharmacist can prescribe other treatments if you are at risk of complications from Flagyl (metronidazole) use

What should I tell my doctor before starting Flagyl?

Tell your doctor if you are allergic to Flagyl (metronidazole) or any ingredients in Flagyl preparations. Also, tell your doctor if you are allergic to tinidazole (Tindamax), secnidazole (Solosec), or other medications.

Give your doctor a complete medical history. Flagyl may not be suitable for people with certain health conditions such as some types of blood conditions, Crohn’s disease, kidney disease, or severe hepatic impairment (liver disease).

Give your doctor a complete list of your current medications, including over-the-counter and prescription drugs, dietary supplements and vitamins, and herbal products. This can help avoid serious drug interactions between Flagyl and other medicines.

Tell your doctor if you are on disulfiram (Antabuse) or have taken this medication within the last 2 weeks. If this is the case, it may not be safe to take Flagyl (metronidazole).

Tell your doctor if you are pregnant, could be pregnant, or plan to become pregnant in the near future, or if you are breastfeeding. Taking Flagyl (metronidazole) during the first trimester (first 3 months) of pregnancy is unsafe.

What precautions should I take while on Flagyl?

Keep all appointments at your doctor’s office. Your doctor may order certain medical tests to check if your infection has cleared or make a dosage adjustment. If you continue to have the same symptoms after finishing the prescribed course of Flagyl, contact your doctor. Do not take the medication for longer than prescribed.

Do not drink alcohol or use any products that contain alcohol or propylene glycol while taking Flagyl (metronidazole) and for at least 3 days after your last dose of the medicine. Propylene glycol and alcohol can interact with Flagyl and cause symptoms such as stomach cramps, nausea, vomiting, sweating, flushing, and headache.

Tell your doctor if you become pregnant while taking Flagyl (metronidazole).

What drugs can interact with Flagyl?

Using Flagyl (metronidazole) with some other medications can affect how the drug works or increase the risk of serious adverse reactions. Your physician may choose a different medication, change the dose or frequency of your medicines, and/or monitor you carefully for side effects if there are known drug interactions.

There can be interactions between Flagyl (metronidazole) and other drugs, such as:

Anticoagulants (blood thinners) like warfarin (Coumadin, Jantoven)
Cimetidine (Tagamet)
Busulfan (Myleran, Busulfex)
Phenobarbital
Phenytoin (Phenytek, Dilantin)
Lithium (Lithobid)

This list does not describe all possible Flagyl (metronidazole) interactions. Give your healthcare provider a complete list of your medications, including prescription drugs, over-the-counter medicines, dietary supplements, vitamins, and herbal remedies. Also, tell your healthcare provider if you smoke, drink alcohol, or use illegal drugs because some of these substances can cause serious health complications when used with prescription drugs.

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