This information is for people who have a child with attention deficit hyperactivity disorder (ADHD). It tells you about clonidine, a treatment used for ADHD. It is based on the best and most up-to-date research.
Does it work?
Possibly. Taking clonidine is likely to help some children control the symptoms of attention deficit hyperactivity disorder (ADHD).
There's less evidence that this treatment works than there is for other medicines, such as methylphenidate or dexamfetamine.
What is it?
Clonidine belongs to a group of drugs that are normally used to treat high blood pressure in adults.
Clonidine is not normally used as a treatment for ADHD in the UK. But a specialist may still prescribe this drug if your child's behaviour does not improve with a stimulant such as methylphenidate or dexamfetamine. (Stimulants are the drugs usually used to treat ADHD.)
Your doctor might prescribe clonidine in addition to a stimulant drug. It may be used to treat the jittery behaviour, irritability, or twitches (tics) that some children have when taking stimulants for ADHD.  
Clonidine (brand name Catapres) comes as tablets.
How can it help?
Treatment with clonidine may help to improve the symptoms of children with ADHD, though some of the studies to show this are not very good.  
There's better evidence that children who are taking a stimulant (dexamfetamine or methylphenidate ) may be helped more by taking clonidine as well.   Clonidine helped improve behaviour and other symptoms of ADHD, but not hyperactivity.
How does it work?
No one knows exactly how clonidine helps control the symptoms of ADHD. But it may stop the brain from making a chemical called noradrenaline.
Experts think that ADHD could be partly due to an imbalance of chemicals in the front part of the brain. It's this part of the brain that controls how you move and feel. By stopping the brain making noradrenaline, clonidine may improve the balance of chemicals and improve symptoms. 
Can it be harmful?
If your child takes clonidine, he or she may feel drowsy and irritable. Clonidine also lowers blood pressure, so your doctor will need to check your child's blood pressure regularly.
One small study involving 24 boys found that some children given clonidine (either alone or with methylphenidate) had a higher risk of developing a slow heart rhythm.  A quarter of boys taking clonidine alone, and half of boys taking both drugs, developed this symptom.
Another study found that children taking clonidine were more likely to have bouts of drowsiness or dizziness than those children taking a dummy treatment (a placebo) although these symptoms went away within six weeks. 
A third study found that children taking clonidine were more likely to have a slow heart rhythm, feel drowsy, or be tired or nervous, compared with children taking a placebo or methylphenidate.