Lenacapavir safety: What you need to know

Health DG Patrick Amoth (in suit) receives the consignment of Lenacapavir at the JKIA on February 17, 2026.

But many people are already asking: How safe is this drug?

Lenacapavir is developed and produced by the American pharmaceutical company Gilead Sciences. While Gilead manufactures the current supply to Kenya, voluntary licensing agreements have been signed with several generic manufacturers, primarily in India, to produce lower-cost versions for low- and middle-income countries by 2027.

The World Health Organization (WHO) monitored the drug's safety during two large clinical trials (2021-2024) involving thousands of participants.

The WHO concludes that lenacapavir is safe, with mostly mild side effects, limited resistance concerns, and no sign of harm in pregnancy. Ongoing monitoring during the use in Kenya will be key, WHO says.

The Guidelines on Lenacapavir (LEN) for HIV Preventionexplain the safety levels observed during the two trials.

 “Overall rates of adverse events were similar between LEN and oral TDF/FTC (a PreP pill), and most events were mild or moderate in severity. Injection site reactions (ISR) were common but typically mild, decreasing in frequency over time without leading to high discontinuation rates,” the guidelines say.

The guidelines explain that injection site reactions, including nodules, pain and redness, were frequently reported in both studies and were generally mild. Nodules are firm, often itchy, or painless subcutaneous lumps that develop days, weeks, or months after injections.

 Injection site reactions were reported both in participants receiving LEN injections and in participants receiving placebo injections in the oral TDF/FTC arms.

In the first major study called PURPOSE 1, 68.8 per cent of people who received LEN reported injection site reactions. In the second study, PURPOSE 2, 83.2 per cent reported such reactions. The report says the reactions became less frequent and less severe over time.

Another concern is drug resistance. Experts reported that two people became infected with HIV while using LEN.

The guidelines state, “Resistance to LEN was analysed among participants who acquired HIV during PURPOSE 1 and PURPOSE 2. In PURPOSE 1, there were no HIV acquisitions in the LEN arm, and thus no cases of resistance were reported.”

The report adds: “In PURPOSE 2, two participants in the LEN arm were diagnosed with HIV, and both had a mutation associated with resistance to HIV-1 capsid inhibitors (N74D). The evidence suggests that LEN use may increase antiretroviral resistance to capsid inhibitors (low certainty of evidence).”

Even so, the WHO says the overall public health impact is limited for now. “Given the overall high efficacy of LEN and the rarity of breakthrough infections, resistance to LEN is unlikely to have a significant public health impact at present. This is because LEN is a first-in-class drug; no other antiretrovirals of this class are routinely used for prevention or treatment.”

Pregnancy safety was also closely studied because many young women took part in the trials.

The guideline reports that the use of Lenacapavir probably has little to no effect in terms of adverse pregnancy and birth outcomes.

 “If women became pregnant, they could continue the study drug, after receiving additional counselling on risks and benefits and giving informed consent,” it says.

 “LEN showed no increase in adverse pregnancy or birth outcomes among the 193 pregnancies reported in PURPOSE 1 so far. No dose adjustment is likely to be required during pregnancy, with pharmacokinetic data indicating standard dosing remains effective.”

In PURPOSE 1, 193 pregnancies were confirmed among women assigned to LEN. The report states that rates of serious pregnancy-related complications were similar between the LEN group and the oral PrEP group. Birth outcomes such as live birth, still birth and miscarriage did not differ significantly.

The guideline adds: “Available data from 184 women with LEN exposure who became pregnant and have outcomes to date suggest that it is possible to rule out a two-fold increase in risk for adverse pregnancy outcomes with a background prevalence of >10% (miscarriage, prematurity, low birth weight), due to the sample size to date. Analysis of pharmacokinetic data suggests that no dose adjustment for LEN is needed during pregnancy.”

While releasing the guidelines in June last year, WHO Director General Tedros Adhanom Ghebreyesus said, “While an HIV vaccine remains elusive, lenacapavir is the next best thing a long-acting antiretroviral shown in trials to prevent almost all HIV infections among those at risk. The launch of WHO’s new guidelines, alongside the FDA’s recent approval, marks a critical step forward in expanding access to this powerful tool.”

WHO advised countries to start rolling out LEN while continuing to monitor safety and resistance. The agency stressed that more data will come as more people use the drug.