Three private medical clinics have been banned from advertising intravenous vitamin drips which claim to help protect against Covid-19.
The Advertising Standards Authority (ASA) said the online posts were a "straight breach" of rules on products sold to treat or prevent disease.
NHS England also said the adverts were misleading and potentially dangerous, and "exploited a worried public".
All three adverts have now been taken down.
Two Instagram posts made in March by Cosmetic Medical Advice suggested that a "super immune system booster" intravenous (IV) drip was an effective way to protect against viral infections.
Another business, Private Harley Street Clinic said on its website that it is possible to boost the immune system by an intravenous infusion of essential vitamins, minerals and amino acids. The firm's Immunobooster IV infusion costs £350 and takes 30 minutes to administer.
Reviv, a company with clinics in Greater Manchester, London and Leeds, also claimed to offer protection against Covid-19. It's website stated: "Help protect and prevent against the new strand of virus (known as the Coronavirus) with a REVIV Megaboost® IV Therapy containing a high dose of Vitamin C."
No treatments have yet been approved by the UK's Medicines and Healthcare products Regulatory Agency (MHRA), meaning that companies cannot make medical claims on their products relating to coronavirus.
The ASA investigations were fast-tracked as part of a focus on prioritising and tackling ads that exploit health-related anxieties during the pandemic.
Jessica Tye, ASA Investigations Manage, told Radio 4's You and Yours that the clinics should not have been making any medical claims in relation to coronavirus.
Reviv told You and Yours that the advert was in a blog post written by a doctor which suggested ways in which vitamin C levels could be increased, including a Reviv treatment, the 'Megaboost' IV therapy.
In a statement, the company said: "The Advertising Standard Authority received two complaints concerned that the blog was suggesting the 'Megaboost' therapy could cure the coronavirus. This is of course, not the case. Having been found in breach of the ASA Code of Conduct we have removed the blog from our site."
A spokesperson from Private Harley Street Clinic said its advert states that "fastidious hygiene and maintaining a strong immune system are key issues in protecting against infections and viruses. At no stage have we made any claims that either of these two measures were medicinal, or could stop a Covid-19 infection. We stated that these were potentially protective measures as part of a healthy lifestyle".
Cosmetic Medical Advice told the BBC it had removed the adverts from Instagram.
IV clinics, or lounges as they are sometimes called, are popping up all over the world, promoted by celebrities. In the UK there are at least 17 IV lounges and 2,500 private clinics which also offer IV therapy.
Clients tend to be younger people aged under 35 who pay to have blends of saline, vitamins and enzymes infused directly into a vein.
The clinics make a number of claims not just that they can boost immunity but also that they can help recovery from a hangover, improve wellness, prevent signs of ageing and even help you burn fat.
NHS England has issued warnings about the use of intravenous vitamin drips and has criticised companies for peddling fake health remedies to the public.
Dr Raj Patel, the Deputy Medical Director of Primary Care for NHS England said there is no evidence to stand up these claims.
"Healthy people do not need intravenous drips of this sort, quite frankly it's exploiting a very worried public".