The company’s shares ticked up on the London Stock Exchange after the FDA approved the drug that will be branded as Mydayis.

Based on the same mixed amphetamine salt active ingredient used in its older Adderall, the new treatment is formulated to last up to 16 hours.

Adderall now has generic competitors and manages symptoms for up to 12 hours. While Shire still has around six years before patents begin to expire on its other ADHD drug, Vyvanse, the Dublin-headquartered company is seeking to ensure its ADHD franchise remains strong.

With its acquisition of Baxalta last year, Shire has been building a presence in rare diseases, but ADHD is still a major part of its business.

Vyvanse and Adderall generated almost $2.4 billion in sales last year, and the company hopes Mydayis could generate annual sales of $500 million by 2020, although analysts’ consensus as compiled by Reuters is around $294 million.

Also known as SHP 465, Shire first tried to get Mydayis approved as long ago as 2006. But it experienced a series of regulatory setbacks until the FDA finally said Shire could refile in 2014.

However the regulator then had a change of heart and said it required more paediatric data before re-assessing the drug.

Mydayis and Adderall both contain amphetamine, a stimulant elevating dopamine, the neurotransmitter associated with motivation, attention and movement.

But these drugs carry a risk of abuse, which is why the FDA is so cautious about approving them.

Shire’s CEO Flemming Ornskov said: "Mydayis is the latest innovation in Shire’s 20-year legacy of helping to support the treatment of ADHD. It’s a testament to Shire’s commitment to helping support the evolving needs of appropriate patients with ADHD."