A chatbot that uses artificial intelligence allows people to simulate a conversation with a dead loved one.
The paid-for service uses information about a person to generate a profile, which users can then interact with.
More than 3,000 in the UK have signed up - most are dealing with the sudden loss of a loved one.
Accredited therapist Billie Dunlevy says it can interrupt the grief cycle.
"There is the possibility that someone could become quite unwell," she continued.