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Half life  – the length of time it takes for half of the drug to be inactivated and excreted.

Health and Safety at Work Act 1974 - a law that means employers are responsible for the health and safety of all their employees.  Employees are also responsible for their own safety and that of their colleagues, and to tell their employer about any condition that might affect this.

Hemiplegia – paralysis of half of the body which happens when one of the hemispheres of the brain is damaged. It affects about 1 in every 1,000 children and can happen before birth or at any time in life. Hemiplegia affects people differently but usually causes a weakness and lack of control in one side of the body, and some learning difficulties. It is also known as ‘hemiparesis’.

Hemisphere – a part of the brain. The brain is made up of a right and a left half: each called a hemisphere. Each hemisphere has four lobes.

Hippocampus – an area in the temporal lobes which is involved in controlling emotion (such as fear or happiness) and instinct (how we respond to certain situations). The area is called hippocampus because it is shaped a bit like a seahorse and ‘hippocampus’ is Greek for seahorse. The hippocampus is the site of the epileptic focus in some people with epilepsy.

Hirsutism – excessive growth of hair on the face, chest and back in a woman. This can be caused by Polycystic Ovary Syndrome and is also a side effect of some AEDs.

Hormones – natural chemicals made in the body that cause changes in the body. For example, some hormones cause puberty (sexual development) or change during pregnancy.

Hydrogen  – a chemical element (the most abundant in the universe). Hydrogen atoms, along with oxygen atoms, make up water.