New York City City Council Speaker Corey Johnson, an out gay man living with HIV, joined other politicians and activists to call on the federal government to break the patent on the drug Truvada.

Truvada is used by people with HIV as part of a treatment regimen, but is also used to prevent HIV infection. It is commonly known as PrEP (Pre-exposure prophylaxis) if used by someone who is HIV negative.

The drug has been proven to be 99% effective in preventing infection. Only two men have contracted HIV while using the drug as prescribed; in both cases, the strain of HIV was resistant to the two medications that make up Truvada.

There have been two other cases of people who had verified adherence to PrEP seroconverting, one in Amsterdam and one in Toronto.

Related: Insurer is sorry it used ‘insensitive language’ when denying PrEP coverage

The drug is also incredibly expensive in the United States. While parent company Gilead Sciences offers programs to lower patient costs and some cities provide the drug to those most at risk of being exposed to HIV, the cost can be prohibitive for anyone without insurance or who doesn’t live in one of the few locations that offer the drug for free.

Some insurers have refused to cover people who take the drug. Earlier this year, Mutual of Omaha announced they will halt their practice of denying health coverage to people using PrEP after being sued for discrimination.

“It’s life or death for people who do not get access to this live-saving medication that they need,” said Johnson said at a news conference held at the city’s AIDS memorial. “Other countries pay $100 year for PrEP. Americans end up paying more than $20,000 a year for the same medication.”

“Gilead Sciences charged over $2,000 a month for a drug that costs them less than $6 a month to make, and whose research was funded entirely by the federal government and other charities,” Christian Urrutia, co-founder of the PrEP4All Collaboration, added.

Because the drug was developed using federal funding, the law provides the National Institute of Health with the option of breaking the patent and allowing generic versions of the drug to come to market.

Activists say if the price of PrEP was lowered dramatically, more people would use it. With more people using the drug, fewer people would be infected with HIV.

According to the Clinton Health Access Initiative, 225,000 people take PrEP in the United States; the majority are men who have sex with men.

Gilead did not respond to a request for comment before publication.