England's healthcare regulator is calling for a change in the law to protect patients using online doctor sites selling prescription-only drugs.
It comes after a BBC Panorama investigation exposed safety concerns relating to websites using doctors from companies based outside England.
The Care Quality Commission said these websites could be "dangerous".
Currently, it can only inspect websites employing doctors contracted by companies in England.
Former doctor Julian Eden set up the UK's first online doctor service called E-Med nearly 20 years ago. In 2009 he was struck off after prescribing through the service to a 16-year-old boy and a woman who became addicted to prescription drugs.
Five years later, together with his now wife, he set up another company called EuroRX, a doctor hire company based in Romania.
Mr Eden can no longer prescribe drugs, but the doctors contracted by his Romanian company can.
Panorama put the quality of the service provided by his doctors to the test with the help of some volunteers. The programme asked them to see if they could buy drugs their own GPs would be highly unlikely to prescribe to them.
Eleanor, who was treated for anorexia when she was a teenager and is completely well now, was able to order three months' worth of prescription slimming pills from one online doctor site.
She filled in a questionnaire giving a false medical history and was asked to pay for the drugs via another Romanian company before her answers were reviewed by a doctor.
The drugs were prescribed by a Romanian doctor hired through EuroRX and delivered within days.
Eleanor said: "I've got so many diet pills here and if I'd still been in the depths of my illness it would have been so dangerous for me."
Prof Helen Stokes-Lampard, chair of the Royal College of GPs, told Panorama: "I'm horrified to see some of those sites that you showed me, to see that you click on the drug first, and then you go through the consultation, and just how easy it was to circumvent the process.
"This isn't right. It's not safe. It has to be sorted."
The site visited by Eleanor cannot be inspected by the CQC because the doctors it uses are contracted by a company based outside England.
Prof Steve Field, chief inspector of general practice for the Care Quality Commission, said: "You should look for the CQC logo because some of these websites, if they are not regulated by the CQC, can be very, very dangerous."
He said they were making sure that patients were safe and getting effective care when a company is based in England.
But he said the law did not allow the CQC "to have any oversight over companies outside England and that is a real problem".
Mr Eden has had several run-ins with the CQC.
E-Med now only sells one drug following inspections by the regulator, prompted by patient safety concerns.
Panorama went undercover posing as potential investors and filmed Mr Eden.
He described the CQC as "idiots" and said he was fed up with regulatory bodies and their auditing rules.
"I'm not gonna do that – if the patient whinges, you give them their money back," Mr Eden said.
Mr Eden later told Panorama that he respects the CQC and has never sought to evade its oversight.
He says his shareholding in EuroRX is simply a sensible business investment in wider markets, all of which are subject to their own regulators.
Celebrity doctor link
Panorama has discovered another UK-based online doctor site using the same Romanian loophole.
UK Meds cannot be regulated by the CQC because it hires doctors to do consultations and prescriptions through its sister company EU General Practitioners in Romania.
The site, which has already made £1.7m profit since it was set up in 2016, is promoted by celebrity doctor Christian Jessen.
Panorama showed the site to Gino Martini, chief scientist for the Royal Pharmaceutical Society.
He said: "As a professional body we do not support promotion of prescription-only medicines.
"What I saw on that website was direct promotion to patients, so it is something we wouldn't support and is something we should really raise with the drug regulators as not being appropriate."
After Panorama wrote to Dr Jessen and UK Meds, the videos featuring him were "temporarily unavailable" before a "clarification notice" was added saying: "This video is for information purposes only. If you have any specific concerns about your health please consult your GP."
UK Meds said the changes to their website were nothing to do with Panorama.
A spokesperson for Dr Jessen told Panorama he was engaged by UK Meds to present short information videos about various medical conditions and that he does not prescribe medication, nor does he endorse a specific product, service or brand.
UK Meds told the programme that patient care and safety is at the core of its business, it is regulated by the UK drug regulator, the MHRA and the General Pharmaceutical Council and complies with all their regulations. It added the doctors it contracts through the Romanian company, EU General Practitioners, are all GMC-registered.
Panorama contacted all relevant UK regulators with the results of its investigation as well as the Department of Health and Social Care.
Prof Field said: "As a GP it makes me very angry that patients are put at risk and as a regulator it makes me even more certain that we need to try and get the legislation changed so that people can't just bypass our regulatory activities."
You can watch Panorama: Online Doctors Uncovered on Monday August 6th 2018, on BBC One at 20.30 and later on BBC iPlayer.