A HIV treatment which is not routinely available on the NHS in England has been dubbed an "essential" medicine by global health leaders.
The World Health Organisation (WHO) has added pre-exposure prophylaxis (PrEP) to its Essential Medicines List.
The treatment, described as a "game changer" in the fight against HIV and Aids, is taken before sex to reduce the risk of getting HIV.
In December last year NHS England announced it would fund a trial of PrEP, with at least 10,000 participants over the next three years.
The announcement followed on from legal proceedings which resulted in the health authority losing a "who pays" legal battle in the Court of Appeal.
Three appeal judges upheld a High Court ruling which said NHS England did have the power to fund the drug despite its pleas that the responsibility lies with local authorities.
Now WHO officials have said that PrEP - taken with tenofovir, alone, or in combination with emtricitabine or lamivudine - should be put on its Essential Medicines List to prevent HIV infection.
Commenting on the news, Dr Michael Brady, medical director at sexual health charity the Terrence Higgins Trust, said: "By including PrEP in this list, WHO have reinforced the effectiveness of PrEP, and its essential role for global heath needs.
"Adding PrEP to our existing HIV prevention strategies, alongside condoms, treatment and regular testing, means we would have everything we need to bring an end to HIV transmission in the UK; where currently 17 people are newly diagnosed with HIV every day.
"Scotland recently made history by becoming the first country to announce it will make PrEP available on the NHS. Wales has also taken a momentous step forward by announcing a three-year pilot that will reach those at risk of HIV.
"However, in England a long-awaited PrEP trial is still yet to materialise, six months after it was promised.
"We must not let PrEP become a postcode lottery – it should be available to all those at risk, as soon as possible, regardless of where they live."
The Essential Medicines List, which was first developed in 1977 and is updated every two years, is used to help countries make decisions about which products they ensure are available for their populations.
"Safe and effective medicines are an essential part of any health system," said Dr Marie-Paule Kieny, the WHO's assistant director-general for health systems and innovation.
"Making sure all people can access the medicines they need, when and where they need them, is vital to countries' progress towards universal health coverage."
Meanwhile, the WHO has also added fentanyl skin patches to the list, saying the move aims to increase access to medicines for end-of-life care.
In March it emerged that NHS officials in England were considering removing fentanyl from the NHS prescription list.
NHS England said it will launch a consultation as it works to develop new national guidelines to stop GPs prescribing medicines and other items which are available over the counter for a fraction of the cost.
The guidelines for clinical commissioning groups (CCGs) will initially be developed around a set of 10 medicines including fentanyl, omega-3 and fish oils, lidocaine plasters, gluten-free foods and travel vaccines.
But NHS England said that the review and recommendation regarding fentanyl does not apply to patches.
A spokesman said: "It would be a mistake to link the current NHS review to the World Health Organisation update because the review and recommendation regarding fentanyl does not apply to patches. Any item that might be appropriate for 'blacklisting' would first be consulted on before changes are made."
Meanwhile, other items added to the WHO's Essential Medicines List included medicines for hepatitis C, tuberculosis and leukaemia.
The list also includes new advice on which antibiotics should be used for common infections and which should be reserved for the most serious circumstances.
Dr Tim Jinks, head of drug resistant infections at the biomedical research charity the Wellcome Trust, said: "To address the serious global problem of drug-resistant infections we urgently need to address inappropriate use of antibiotics.
"The updated Essential Medicines List should help ensure antibiotics of last resort are reserved only for when first line treatments will not work and that doctors in all countries have easy access to the best and most appropriate treatments."