Late-night messages sent to shoppers with mental health problems leave them vulnerable to financially-crippling impulse buys, a report has suggested.
They felt they were unfairly targeted with email marketing and TV shopping at night when their defences were down.
The report's authors, the Money and Mental Health Policy Institute, said shoppers should be allowed to set "opening hours" for online accounts.
A retailers' trade body said no shop deliberately targeted the vulnerable.
Internet shopping is valued at £1bn every week, with sales representing about 15% of all retail activity in the UK.
The report said that 24-hour online shopping meant "consumers who struggle to control their spending find themselves at greater risk than ever before".
Retailers send personalised emails to customers, based on previous purchases, which may include short-term discounts and promotions.
The report claimed that while most retailers targeted their marketing for first thing in the morning - from 06:00 to 09:00 - or early evening - from 17:00 to 22:00, a few seemed to frequently send emails at night - from midnight to 05:00.
Some mental health problems manifest themselves in compulsive buying, making purchases which are later regretted and could lead them into a spiral of debt.
So-called crisis spending often occurs during periods of poor mental health and was "motivated by emotional or psychological needs and processes rather than material need", the report said.
"Some people experiencing mental health problems find it difficult to return online purchases. They often feel too ashamed or guilty about their behaviour, or may face practical barriers such as social phobia preventing them from going to the post office."
The institute called for:
- Settings to allow people to restrict online shopping to certain hours
- Options to delay delivery until a confirmation is entered in the morning
- A chance to opt-out of marketing specifically sent at night
- The chance to block shopping channels on TVs
Bryan Johnston, from the British Retail Consortium, which represents retailers, said: "This report raises some serious issues which retailers consider carefully, but no retailers deliberately target vulnerable customers.
"The timing of marketing varies greatly, but mails are generally timed to land when they are most likely to be seen and never with a view to exploiting a particular vulnerability. All customers are able to opt out of marketing, which for many delivers useful product news and special offers."