The typical dose for bacterial vaginosis is one 400mg metronidazole tablet taken twice a day. Alternatively, a one-day course of metronidazole, totaling 2000mg (2g), may be prescribed. Your doctor will provide guidance on the appropriate dosage for you.

Common side effects include:

• Nausea or vomiting
• Diarrhoea
• Metallic taste in your mouth
• Furry tongue

Very rare side effects include:

• Confusion
• Hallucinations
• Seizures
• Sleepiness
• Dizziness
• Headache
• Blurred or double vision
• Dark-colored urine
• Muscle or joint pain

Other possible side effects:

• Numbness, tingling, or weakness in the arms or legs
• Loss of appetite
• Fever
• Eye pain
• Hearing loss
• Ringing in the ears
• Skin rash

Serious side effects – seek immediate medical help (call 999 or go to A&E) if you experience:

• Swelling of the hands, feet, lips, or throat
• Difficulty breathing
• Itchy skin rash (hives) or nettle rash (urticaria)
• Skin rashes with blistering, peeling, or bleeding around the eyes, mouth, nose, and genitals
• Stiff neck, headache, hallucinations, speech issues, and confusion

Also contact your doctor if you experience:

• Unexpected infections, mouth ulcers, bruising, bleeding gums, or extreme tiredness
• Yellowing of the skin and eyes (jaundice)
• Severe stomach pain (pancreatitis)

You can find a full list of side effects in the patient information leaflet included with your medication.

How long do metronidazole side effects last? Side effects are usually short-lived, with most appearing within 30 minutes of taking the 400mg tablet and lasting a few hours. You may experience them with each dose.

If side effects persist and impact your daily life, consult your doctor.

What to do if you experience side effects: Taking metronidazole with food may help reduce some side effects. If side effects become intolerable, consult your doctor, who may adjust your dose or suggest an alternative treatment.

You can report any side effects, even those not listed in the leaflet, to the Yellow Card Scheme.

Do not take metronidazole tablets if you are allergic to any of the ingredients listed in the medication.

Before taking metronidazole tablets, inform your doctor if you:

• Have or have ever had liver problems
• Have a disease that affects your nervous system
• Are receiving kidney dialysis
• Are taking any prescribed, over-the-counter, or herbal remedies

You should also inform your doctor if you are taking any of the following medications:

• Anticoagulants (e.g., warfarin, aspirin) to thin the blood
• Lithium
• Epilepsy medications (e.g., phenytoin, primidone, phenobarbitone)
• Busulfan (for leukaemia)
• 5-fluorouracil (for cancer)
• Ciclosporin
• Disulfiram

Metronidazole and pregnancy: If you are pregnant, think you may be, or are planning to become pregnant, consult your doctor. Metronidazole should only be used during pregnancy when necessary.

Metronidazole and breastfeeding: Avoid breastfeeding while taking metronidazole, as small amounts of the medication may pass into breast milk.

Metronidazole and alcohol: Do not drink alcohol while taking metronidazole, as it can cause unpleasant side effects such as nausea and vomiting. Avoid alcohol for the duration of the treatment and for 48 hours after completing the course.

At Superdrug Online Doctor, we offer a range of alternative treatments for bacterial vaginosis, including:

• Zidoval: A prescription-only antibacterial gel containing metronidazole. Instead of tablets, this gel is applied inside the vagina to treat the infection.

• Dalacin Cream: A cream containing clindamycin, applied inside the vagina to stop the growth of the bacteria causing bacterial vaginosis. Available with a prescription.

• Fluomizin: An antiseptic antimicrobial tablet that is inserted into the vagina using an applicator. Fluomizin is typically recommended as an alternative to clindamycin cream when it is unsuitable or ineffective.

Metronidazole tablets do not interfere with any type of contraception. However, if you experience vomiting or diarrhea while taking metronidazole, the effectiveness of the contraceptive pill may be reduced. If you have concerns about using contraception while taking metronidazole, it's best to consult a healthcare professional for personalized advice.

• Bacterial Vaginosis: Learn More – Which Treatments Are Effective in Bacterial Vaginosis? NIH [accessed 22 July 2024]
• Common Questions About Metronidazole NHS [accessed 22 July 2024]
• Impact of Oral Metronidazole Treatment on the Vaginal Microbiota and Correlates of Treatment Failure NIH [accessed 22 July 2024]
• Metronidazole BNF [accessed 22 July 2024]
• Metronidazole 400 mg Film-Coated Tablets EMC [accessed 22 July 2024]
• Metronidazole 200 mg Film-Coated Tablets EMC [accessed 22 July 2024]
• Oral Metronidazole NICE [accessed 22 July 2024]
• Side Effects of Metronidazole NHS [accessed 22 July 2024]