Barrows, who advises companies on financial crime and its various guises, said: "If there's a chance to make money out of something, scammers will be the first in the queue to do it - and a big thing like these weight loss drugs is too good an opportunity to miss."
He said he had used online tools to investigate the Facebook profile page of one of the so-called doctors sharing the weight loss adverts.
Using an image search, he was able to discover the profile photo of the doctor originated back to a woman shown in a Romanian bank advert.
Barrows said the advert also claimed that the weight loss patches were "made in the UK", but said the package held up in the video "clearly has the French flag".
He said another indication that "things didn't add up", was that the 1,000 followers to the doctor's Facebook profile page were entirely from Vietnam. He said clues like this should help people spot fake accounts.
"The point is, the people selling this stuff are trying to bypass your rational response, they want you to really want to buy this stuff because you want to lose weight and it's so easy when that emotion takes you over to stop thinking clearly and just think 'oh yeah this is for me', and then spend your money," Barrows said.
He urged people to do "basic checks" on products before making any purchases.
Guy's and St Thomas' NHS Foundation Trust said they hoped that anyone finding the videos online would report them to the social media platforms where they were being shared.