By Maggie Fick

LONDON (Reuters) - Britain's pharmacies regulator on Tuesday tightened rules for online pharmacies' prescribing obesity drugs, ordering them to make changes to prevent people from receiving drugs that could cause them harm. 

The General Pharmaceutical Council (GPhC), which regulates UK pharmacies and has the power to ban them from supplying medicines, said it has updated its overall guidance to online pharmacies for the first time in three years, mainly because of its concerns about how some dispense weight-loss drugs.

The regulator also added the GLP-1 receptor agonist drug class, which includes weight-loss injections Wegovy and Mounjaro, to its list of "high-risk medicines" that require pharmacies to use extra measures when prescribing.

Others in this category include medicines deemed liable to misuse, like opioids and sedatives, antibiotics, and those used for long-term conditions such as asthma and diabetes.

The online market for obesity drugs has boomed in the UK.

Late last year, several online pharmacies told Reuters they estimated as many as 500,000 people were taking the drugs via the private market in the UK, far more than the number receiving the medicines in the state-run National Health Service.

"We have seen, through our inspections and concerns raised by the public, some concerning ways in which these drugs were being supplied online and we have taken action as a result," Louise Edwards, Chief Strategy Officer at the GPhC, told Reuters.

Since 2021, the regulator has taken enforcement action against at least a dozen online pharmacies over their supply of weight-loss medicines, she said.

The guidance requires online pharmacies to "independently verify the person's weight, height, and/or body mass index" before prescribing a weight-loss drug to them. This could be through a video consultation, accessing the person's clinical records or contacting the person's doctor, the guidance said.

Under the new guidance, online questionnaires will no longer be considered sufficient verification for prescribing obesity drugs, and neither will a phone call.

Wegovy is made by Danish drugmaker Novo Nordisk and Mounjaro is made by U.S. pharma giant Lilly. The companies are first-to-market with weight-loss drugs that have propelled them both to record profits.

The World Health Organization said in December the drugs had the potential, along with other health interventions, to tackle a global obesity crisis.

(Reporting by Maggie Fick; editing by Barbara Lewis)