Thanks to a court ruling in the UK, a cheaper generic version of PrEP could be available in the future, but in the United States, only 4% of men who have sex with men are using the drug — and cost is a big culprit.

PrEP has shown itself to be remarkably effective in halting the transmission of HIV.

Britain’s High Court has overturned Gilead Science’s patent extension on Truvada, the brand name for PrEP. This could lead to a less costly generic version of the medication. For those in the UK, this could lead to an 80-90% savings in cost.

PrEP is not yet available via the National Health Service in England and Wales, in part due to the cost. At current, the NHS would have to pay as much £350 every month for each person using the drug.

A similar barrier to cost exists in the US, and it is likely keeping the drug out of the hands of those who could use it the most.

In a recent study published in PLOS ONE, researchers showed that the use of the PrEP is still extremely low in the US. The blame is put on difficulties in acquiring the medication, including its cost, as well as a lack of knowledge about the effectiveness of the drug.

Most in the study reacted positively to the drug, but this didn’t translate into usage, with bisexual men even less likely to take it over gay men.

The ruling in the UK — as well as a similar case in Ireland last year — could help fuel activists seeking similar options in the US.

A campaign titled #breakthepatent is pushing for generic PrEP in the United States. According to drugs.com, a 30-day supply of the brand-name drug could cost around $1,758, depending on the pharmacy you use.