Prof Mackey said: ‘It was clearly the easiest study the pain centre at Stanford has ever recruited for. When you’re in love you want to tell everybody about it.

‘We intentionally focused on this early phase of passionate love. We wanted subjects who were feeling euphoric, energetic, obsessively thinking about their beloved, craving their presence.

‘When passionate love is described like this, it in some ways sounds like an addiction. We thought ‘maybe this does involve similar brain systems as those involved in addictions which are heavily dopamine-related.’