The app, called 'Silver Linings', allows psychosis patients to keep a diary to track their medication, mood, well-being and build coping strategies.
It has been developed by Birmingham and Solihull Mental Health NHS Foundation Trust (BSMHFT) and Bristol-based startup Appadoodle since June last year. It is currently being trialled by a group at the trust and is due to launch next month.
The app works by users signing in, creating an avatar, and answering a series of personalised questions about topics like their medication, mood, diet and wellbeing.
'Silver Linings' has a smart algorithm so it can provide feedback and advice, and track changes over time.
It is tailored to each individual, so people can set their own metrics for recovery and which issues, such as paranoia or not sleeping, are most important to their mental wellbeing.
The app, which is primarily aimed at 16 to 24-year olds, uses a series of 'gamification' style rewards like unlocking achievements, badges and accessories, thus rewarding patients who use it more frequently.
"There is a big gap between appointments, when patients see a doctor or nurse to discuss how they're getting on with their illness," Appadoodle's managing director Jamie Prangnell explained.
"This app gives more smart data to fill in the gaps of how they're doing while they're away from meetings."
BSMHFT psychiatrist Dr Erin Turner, who is leading the project, hopes the app will encourage young people to engage with their treatment and take control over their recovery, helping them to get better quicker.
It also gives clinicians access, with patients' permission, to data on the individual's mood and associated causes, thanks to an easy-to-navigate dashboard area featuring graphs, pie charts and other visualisations.
The inspiration for 'Silver Linings' originally came from Turner as a way to better engage young patients in their treatment, instead of relying on leaflets and packs that often go unread.
"It's not just about imparting information, but engaging young people in their recovery. We're really looking at them taking responsibility for some of their symptoms and self-monitoring.
"Then from my perspective as a doctor, it's the importance of engaging in treatment and medication," she explained.
It was funded by an NHS innovation grant and other trusts have already been in touch to ask about the app, Turner said.
If successful, BSMHFT and Appadoodle plan to create a wider range of apps to support the treatment of other mental health conditions.
"This is definitely just the first step, there is lots we want to do to develop it further, like tracking physical health, given how linked that is to mental health. We've had lots of positive reactions, but we know there are plenty of things that will need to be improved," Turner added.
Explaining the name 'Silver Linings', she said: "We spoke to patients to try to get a nice catchy name, something that instilled hope. And we hit on the phrase 'every cloud has a silver lining'.
"We wanted something inspirational, because psychosis is often just a temporary illness. Many patients recover fully."