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 towards your palm.
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 your GP can help and self-help.
Ménière's disease is a rare disorder that affects the inner ear. It can cause vertigo, tinnitus, hearing loss, and a feeling of pressure deep inside the ear.
Mesothelioma is cancer of the lining that covers most of the body's organs. It's usually caused by asbestos exposure. Find out about the symptoms, causes, treatments and outlook.
Find out what metabolic syndrome is, what the symptoms and risk factors are, and what you can do to reverse or prevent it.
Find out what can cause a metallic taste in the mouth and when to see a GP. It can be a symptom of many different things. Any recommended treatment will depend 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.
Motion sickness is a term that describes an unpleasant combination of symptoms, such as dizziness, nausea and vomiting, that can occur when you're travelling.
Read about mouth ulcers, including what they look like, what causes them, how to treat them, and how to avoid getting them.
Find out what MRSA is, how you get it, what the symptoms are, and how it's treated.
Find out about multiple system atrophy, including information about symptoms, causes, diagnosis and treatment.
Find out about the risk of Mycobacterium chimaera infection after open heart surgery, including what to do if you're at risk and what the symptoms are.
Find out about myelodysplastic syndrome (myelodysplasia or MDS), a blood disorder that causes a drop in the number of healthy blood cells.
Find out about myositis, including the different types of myositis, how it's diagnosed and treated and the possible complications.
Malaria is a serious tropical disease spread by mosquitoes. If it is not diagnosed and treated promptly, it can be fatal.
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.
Read about mastitis, a condition that causes a woman's breast tissue to become painful and inflamed. It can usually be treated easily, but it's important to see your GP if you think you have it.
Read about mastocytosis, a rare condition caused by an excess number of mast cells gathering in the body's tissues.
Read 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.
Read about meningitis, an infection of the protective membranes that surround the brain and spinal cord. Find out about the symptoms, vaccines and treatments.
The menopause is when a woman stops having periods and is no longer able to get pregnant naturally. Read more about the symptoms, causes and treatments.
A migraine is usually a severe headache felt as a throbbing pain at the front or side of the head.
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.
Read about moles, including what a normal mole looks like and checking with a GP if you notice a change in the appearance of a mole. Also, find out how to prevent a mole becoming cancerous.
Molluscum contagiosum is a usually harmless infection that causes small dimpled spots to appear on the skin.
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.
Read about mouth cancer, also known as oral cancer, including information about symptoms, types, causes, treatment, possible complications and reducing the risks.
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.
Read about ways to help treat mucositis, a common side effect of cancer treatments, which causes pain and inflammation in the mouth and gut.
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.
Find out about Munchausen's syndrome, a disorder where someone pretends to be ill or induces symptoms of illness in themselves. Munchausen's by proxy is where a person fakes or induces illness in someone under their care.
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.
Monkeypox is a rare disease caused by infection with the monkeypox virus. Most cases have been in Africa. The risk of catching monkeypox in the UK is very low.
Information from the NHS website on medical cannabis
Advice and support from the NHS for common problems like stress, anxiety and depression