Bacterial vaginosis (BV) is a common cause of unusual vaginal discharge. It happens when the natural balance of bacteria in your vagina changes.

If you have BV, you might notice:

• discharge with a strong fishy smell, especially after sex
• discharge that's thinner, more watery or greyish-white

BV doesn't usually cause itching or soreness. If you have these, it could be something else, like thrush.

It's not fully understood why the balance of bacteria in the vagina changes, but BV is more common in people who are sexually active. However, you can still get BV if you've never had sex.

Factors associated with BV include having a change of sexual partner, and douching or using perfumed products in or around the vagina, like shower gels or deodorants.

Always take metronidazole exactly as prescribed.

• 7-day course: one 400mg tablet, taken twice a day for 7 days
• Single dose: five 400mg tablets, taken at one time

Swallow your tablet(s) whole with a drink of water. Don't crush or chew them. Take them during or just after a meal. Keep taking them until you've finished the course, even if you feel better.

If you forget a dose, take it as soon as you remember. If it's nearly time for your next dose, skip the one you missed. Don't take a double dose to make up for it.

If you take too many tablets, contact a doctor or go to A&E straight away. Take the medication pack with you.

BV is treated with antibiotics. Metronidazole is an antibiotic that stops the growth of the bacteria linked to BV.

Many people start to feel better within a few days. Keep taking your treatment until you've finished the course, even if you feel better. This helps stop BV coming back.

No. BV isn't classed as a sexually transmitted infection (STI). But sex can trigger it, and it can be passed on during sex to anyone with a vagina. If your partner has a vagina, they may need treatment too.

Having BV can make it easier to catch an STI. If you've had a new partner, it's a good idea to get tested at a sexual health clinic.

BV is usually treated with antibiotic tablets, or a gel or cream you put into your vagina. At MedExpress, we offer:

• Metronidazole: antibiotic tablets
• Dalacin (clindamycin): antibiotic cream
• Zidoval (metronidazole): antibiotic gel

Like all medications, metronidazole tablets can cause side effects, although not everyone gets them. These include:

• Feeling or being sick (nausea)
• Diarrhoea
• An unpleasant taste in your mouth

Metronidazole can make some people feel drowsy or dizzy, or affect their eyesight. If this happens, don't drive or use machinery.

Call your GP or 111 if:

• Your skin or the whites of your eyes turn yellow
• You experience extreme tiredness, bleeding gums, bruising, mouth ulcers or unexpected infections
• You experience severe stomach pain, which may radiate to your back
• You experience a skin rash that blisters or peels
• You experience blurred or double vision

Call 999 or go to A&E if:

• Your lips, tongue, mouth or throat swell up, or you're struggling to breathe. These may be signs of a serious allergic reaction (anaphylaxis).
• You have a high temperature, headache and stiff neck, together with feeling or being sick and finding bright light hard to look at.
• You experience hallucinations (seeing or hearing things that aren't there), confusion, or problems speaking or moving your arms or legs.

You can report side effects through the MHRA Yellow Card scheme.

No. Don't drink alcohol while you're taking metronidazole tablets, or for 2 days (48 hours) after your last tablet. This gives the medicine time to leave your body.

Alcohol and metronidazole can react and make you feel very unwell. You might feel or be sick, or get stomach pain, hot flushes, a racing heartbeat or a headache.

Always read the patient information leaflet before commencing treatment.