A macular hole is a small gap that opens at the centre of the retina in the macula. It causes blurred and distorted vision, and can be treated with surgery.
Find out what a magnesium test is and when it might be used.
Mallet finger is an injury to the end of the finger that causes it to bend inwards. Find out about the condition, its treatment and causes.
Maple syrup urine disease (MSUD) is a rare but serious inherited condition. It means the body can't process certain amino acids.
Find out about mastoiditis, a serious bacterial infection that affects the mastoid bone behind the ear.
MCADD is a rare genetic condition where a person has problems breaking down fat for energy. Read about the symptoms, causes and outlook.
Find out about medically unexplained symptoms, including possible causes, the connection between physical and mental health, how a GP can help and self-help.
Find out more about Ménière's disease, a rare condition that affects the inner ear.
Find out about the symptoms, causes and treatments of mesothelioma, a cancer of the lining that covers some of the body's organs.
Find out about metabolic syndrome, what it is, how it's diagnosed and how to prevent and treat it.
Find out about metallic taste in the mouth. It can have lots of possible causes and how you get rid of it depends on the cause.
Find out about the problems that can affect the heart's mitral valve, including prolapse, regurgitation and stenosis. Also, read about the different types of mitral valve surgery.
A molar pregnancy is when there's a problem with a fertilised egg, which means a baby and a placenta do not develop the way they should after conception. A molar pregnancy will not be able to survive.
Morton's neuroma is a condition that affects the nerves between the toes. Find out about the symptoms, causes and treatments.
Find out more about motion sickness, an unpleasant combination of symptoms, such as dizziness, feeling sick, or being sick, that can happen when you're travelling.
Find out about mouth ulcers, including what they look like, what causes them, how to treat them, and how to avoid getting them.
Find out about MRSA, which is a bacteria that usually lives harmlessly on the skin but can cause a serious infection if it gets inside the body.
Find out about multiple system atrophy, including information about symptoms, causes, diagnosis and treatment.
Find out about myelodysplastic syndrome (myelodysplasia or MDS), a blood disorder that causes a drop in the number of healthy blood cells.
Find out more about myositis, the name for a group of rare conditions that cause muscle weakness.
Find out about the causes of missed or late periods and when to seek medical help.
NHS information about meniscus tears (knee cartilage damage), including symptoms, how to ease symptoms yourself and when to get medical help.
Find out about myalgic encephalomyelitis, also known as chronic fatigue syndrome or ME/CFS. It’s a long-term condition with a wide range of symptoms. Extreme tiredness is the main symptom.
Find out more about malaria, including where it's found, how you catch it and what the symptoms are.
A malignant brain tumour is a fast-growing cancer that spreads to other areas of the brain and spine.
Find out about malnutrition, including the signs and symptoms, who's at risk, when to see a GP, and how it's treated.
Find out what Marfan syndrome is, what causes it, plus how it's diagnosed and treated.
A mastectomy is an operation to remove a breast. It's used to treat breast cancer in women and men.
Find out about mastitis, including what the symptoms are, how to treat it and why it happens.
Read about mastocytosis, a rare condition caused by an excess number of mast cells gathering in the body's tissues.
Find out about measles, a highly infectious viral illness that can be very unpleasant and sometimes lead to serious complications.
As medicines are a crucial part of medical treatment, it's important to have a good understanding of them.
Find out about melanoma skin cancer, including what the symptoms are, what causes it and how it’s diagnosed and treated.
Read about meningitis, an infection of the protective membranes that surround the brain and spinal cord. Find out about the symptoms, vaccines and treatments.
Find out about menopause symptoms, causes and treatments, and things you can do to help.
Find out about migraines, including symptoms and how they're treated.
A miscarriage is the loss of a pregnancy during the first 23 weeks. The main signs of a miscarriage include vaginal bleeding, followed by cramping and pain.
Find out about moles, including what a normal mole looks like and when a mole could be serious. Also, find out how to prevent a mole becoming cancerous.
Find out about molluscum contagiosum, including what the symptoms are and what to do if you think you or your child have it.
Read about motor neurone disease (MND), a rare condition where parts of the nervous system become damaged. This causes increasing weakness, and in many cases, muscle wasting.
Magnetic resonance imaging (MRI) is a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body.
Find out about mucositis, including what the symptoms are, what you can do to ease them, when to get medical help and what treatments are available.
Find out more about multiple myeloma, also known as myeloma, a type of bone marrow cancer.
Multiple sclerosis (MS) is a condition that can affect the brain and spinal cord, causing a wide range of potential symptoms, including problems with vision, arm or leg movement, sensation or balance.
Mumps is a contagious viral infection that used to be common in children before the introduction of the MMR vaccine.
The muscular dystrophies (MD) are a group of inherited genetic conditions that gradually cause the muscles to weaken, leading to an increasing level of disability.
Read about myasthenia gravis, including the symptoms and when to see a GP. Also, find out what causes the condition, how it's treated and the outlook.
NHS information about memory loss (amnesia), including advice about what to do if you have problems with your memory and what the cause might be.
Find out about Middle East respiratory syndrome coronavirus, a rare but severe respiratory illness.
Find out about mpox (previously known as monkeypox), including how you get it, what the symptoms are and what to do if you think you have it.
Information from the NHS website on medical cannabis.
Find out about mouth cancer, including what the symptoms are, what to do if you think you have it, how it is treated, and where to get support.
Find out about Munchausen's syndrome, a disorder where someone pretends to be ill or induces symptoms of illness in themselves.
Find out about the MenACWY vaccine, including what it’s for, who should have it, how to get it and possible side effects.
Find out about the MenB vaccine, including who should have it, how to get it, side effects and how well it works.
Find out about the MMR vaccine for measles, mumps and rubella, including who should have it, when it's given and possible side effects.