macrophage – large white blood cell that engulfs or ‘eats’ infectious organisms and waste material from dead cells.

major mutation – a drug resistance mutation that have a big impact on whether a drug continues to work. This used to be called a primary mutation.

malaria – a parasite infection of red blood cells.

malignant – dangerous. A malignant cancer is a dangerous cancer that is growing.

matched – in clinical trials matched refers to each group having similar age, gender, ethnicity, HIV duration, health etc in a study.

maternal-foetal microtransfusions are when small amounts of infected blood from the mother leak from the placenta to the baby during labour (or other disruption of the placenta).

mean (average) – where all the results are added together, and then divided by the number of results to find the (mean) average. See median.

What is an average.

median (average) – where the results are all arranged in numerical order and the middle of the range is taken as the (median) average. See mean.

What is an average.

mega-HAART – a term for a drug combination that uses five or more HIV drugs, usually including 2–3 protease inhibitors. Rarely used now.

meningitis – inflammation (-itis) of the meninges (part of fluid that surrounds the brain). Meningitis can be caused by different infections – ie bacterial meningitis (from bacterial infection), viral meningitis (form a virus) etc.

methadone – a man-made opiate that used to treat heroin addiction. See also buprenorphine.

mg (milligram) – abbreviation for milligram. 1000 milligrams = 1 gram.

microbicide – a gel that may protect against infection.In reference to HIV, this is usually referring to a gel that could be applied before sex. In 2010 a study called Caprisa 004 provided the first evidence that a microbicide (in this case a gel containing the HIV drug tenofovir) might protect against HIV infection.

Minimum Effective Concentration (MEC) – the lower level of a drug in the body that will still be effective.

What happens when you take a drug?

minor mutation – a drug resistance mutation that have a big impact on whether a drug continues to work. This used to be called a secondary mutation.

mitochondria – energy producing factories that live inside other cells.

mixed feeding – combination of breastfeeding and bottle feeding.

mL (millilitre) – a measure of a volume of liquid. 1000 millititres = 1 litre.

monoinfection – infection with only one virus

monotherapy – using only one drug.