The European Commission granted a marketing authorisation valid throughout the European Union for Intuniv on 17 September 2015. The active substance in Intuniv is guanfacine. Intuniv is used to treat attention deficit hyperactivity disorder (ADHD) in children and adolescents aged 6 to 17 years when stimulant medicines are not appropriate or do not control their symptoms well enough. The way Intuniv works in ADHD is not established. It is thought that the active substance, guanfacine, might influence the way signals are transmitted between cells in areas of the brain called the prefrontal cortex and basal ganglia by attaching to certain receptors that are heavily concentrated in these areas. Several studies have shown Intuniv improving ADHD symptom scores (ADHD-RS-IV) in children and adolescents. In a study of 337 children aged 6 to 17 years, the reduction in ADHD symptoms with Intuniv treatment after 10 to 13 weeks was 24 points compared with a reduction of 15 points seen with placebo (a dummy treatment) and 19 points seen with atomoxetine (an ADHD medicine). In another study of 312 adolescents aged 13 to 17, the reduction in ADHD scores at 13 weeks was 25 points with Intuniv and 19 points with placebo. Two other short-term studies involving 631 patients also showed Intuniv at various doses improving ADHD scores more than placebo. Intuniv was also evaluated in terms of treatment failures (based either on worsening of ADHD symptoms or patients stopping treatment). In a long-term maintenance study in 301 children and adolescents aged 6 to 17 years treatment failures occurred in 49% of patients taking Intuniv compared with 65% of those taking placebo. The most common side effects with Intuniv are sleepiness (in nearly half of all patients), headache (in more than a quarter), tiredness (in about 1 patient in 5), and upper abdominal pain and sedation (both in around 1 in 10). Sleepiness usually begins at the start of treatment and lasts for 2 to 3 weeks. More serious side effects are less common and include: low blood pressure and weight gain (both in around 1 patient in 30), slow heart rate (1 in 60) and fainting (in less than 1 in 100).