An estimated 1.2 million Americans are living with HIV infection, including 156,300 people who do not know they are infected. It seems unusual that Truvada, an effective, once-a-day pill to prevent HIV infection, is not used by many people. Why not — what’s the deal with this drug?

Years ago, the HIV/AIDS community undoubtedly would have hailed this pre-exposure prophylaxis (PrEP) as a miracle pill, with news and praise spreading far and wide. As described by The Medical Letter, Gilead Sciences Inc., created Truvada by combining two separate antiretroviral drugs used to treat HIV infection, emtricitabine and tenofovir disoproxil fumarate. Originally, the Food and Drug Administration (FDA) approved Truvada for treating an HIV infection in 2004. The drug works by blocking an enzyme, HIV reverse transcriptase, and this enzyme obstruction prevents the virus from making copies of itself in an infected person’s body.

Less than a decade later, in 2012, the FDA indicated the pill might also be used prophylactically to help adults who are at high risk of sexually acquiring HIV. This second FDA approval was based on studies conducted on high-risk patients. In one, 2,499 HIV-negative men who have sex with men reduced the risk of HIV by 87.5 percent. Another trial included 4,747 heterosexual couples where one partner was HIV-infected and the other was not; here the researchers found risk reduced by 75 percent. More recent studies listed on the Centers for Disease Control and Prevention website suggest the potential decrease in infection risk is more likely 92 percent.

Importantly, even before the FDA approved Truvada as a PrEP, gay men had been using the drug off-label based on the CDC's recommendation. In fact, the CDC says one in every four sexually active men who have sex with men, one in five people who inject drugs, and one in 200 heterosexually-active adults fit the recommended guidelines and so might benefit from using the drug. While information on the total number of PrEP users is incomplete, only 3,253 people had started the PrEP regimen between Jan. 1, 2012, and March 31, 2014 according to PBS (based on Gilead's survey of half the pharmacies that dispense the drug).

Successful, But No One's Heard About It

Why such small numbers? You may suspect side effects as the prime culprit here, but Truvada has shown little downside in that regard. Early on in the clinical trials, some people had minor side effects, such as an upset stomach or a loss of appetite, but these usually went away within the first month. Other people report a mild headache, while in a recent National Institutes of Health study reported by Medical Daily, kidney issues forced one in 200 people to temporarily stop taking the pill, yet after a couple of weeks, these patients resumed treatment with no ill effects.

Could it be a money matter? That's likely part of the reason for the low use of PrEP. A 30-day supply of Truvada costs about $1,160, with the co-pay required by some insurance plans ranging as high as $1,300 per year, Bloomberg reports. More than a few people would find such costs prohibitive, while for others, it simply goes against the grain to take (and pay for) drugs when you're still healthy. These combined factors led Gilead itself to predictions of a decade passing before PrEP becomes widely used in the U.S., The New Yorker reported, and by then Truvada could be off patent (and open to generic copy cat pills). Access to generic versions would benefit patients, but Gilead not so much.

Decline in Condom Use?

Though side effects and money dissuade some from taking PrEP, others argue the real problem is doctors simply don’t know about the medicine. This claim has been made by The St. Louis Post-Dispatch, among other media outlets. In its recent article, a patient interested in taking the drug — he'd seen friends posting about it on Facebook — called around and found many doctors were not familiar with the drug. This same article contends other professionals who might be acquainted with the treatment either fail to discuss it with patients or actively discourage its use based on their fears that PrEP might lead to a decline in condom use and cause a spike in other sexually transmitted infections.

One final issue with PrEP is sticking with the program by taking the pill each and every day. As explains, intermittent PrEP — taking the pill for a few days or weeks, stopping, and then starting again — decreases its effectiveness greatly. The NIH found 21.5 percent of people enrolled in its trial program didn’t stay for the duration. More generally, drug adherence is an issue with all medicines as real life has a habit of getting in the way.

While PrEP neglect may be caused by a whole host of issues, the hopeful still see Truvada as a success story just waiting to happen. With 50,000 new HIV infections occurring each year, a substantial market for this once-a-day pill already exists. Once the patent expires, generic drug manufacturers will most certainly swoop in for business.