What are the side effects of PrEP tablets?

Taking PrEP (pre-exposure prophylaxis) to protect yourself against HIV is safe and effective. While injectable options now exist, daily or on-demand pills remain the most popular choice.

Today, there are two main PrEP pills: Truvada (tenofovir disoproxil / emtricitabine), the most well-known, and Descovy (tenofovir alafenamide / emtricitabine), a newer option. Both provide outstanding protection, but they interact with the body in slightly different ways.

Short-term side effects

A small number of people experience mild symptoms during the first month. This can include a mild headache, nausea, tiredness, or diarrhoea. In the large DISCOVER trial comparing both pills, diarrhoea was the only side effect reported by more than 10% of users, and symptoms typically disappeared on their own within the first few weeks.

A practical tip: taking your pill with food, especially a meal containing some fat, may help reduce side effects such as nausea and stomach upset.

Longer-term side effects

Because PrEP is taken over months or years, clinics monitor your health over time. Most people experience no long-term problems, but healthcare providers pay particular attention to kidneys, bones and metabolic changes.

• Kidneys: Kidney function naturally declines as we get older, so people over 40 or 50 are more likely to have underlying kidney changes before even starting PrEP. Truvada can cause small, reversible dips in kidney function. In a major Australian study, only 0.6% of users had kidney issues after a year, and it was almost non-existent in people under 40 (less than 0.1%). Descovy was designed to enter cells directly, leaving about 90% less medication floating in the bloodstream. In clinical trials, kidney markers stayed stable or improved over nearly three years in people taking Descovy. This makes Descovy the preferred choice for anyone with existing kidney concerns. If you take Truvada on demand (the '2-1-1' method), that also reduces kidney exposure compared to daily dosing.
• Bones: Truvada can cause a slight dip in bone density (1 to 2%). While this reverses in adults once they stop taking the pill, our bones continue building peak strength until our early twenties. Studies show that bone changes in teenagers on Truvada might not fully recover. Descovy, on the other hand, maintains or slightly increases bone density. Because of this, guidelines recommend Descovy for young people under 18 and anyone with osteoporosis.
• Weight and cholesterol: Neither pill causes abnormal weight gain. Instead, the older pill (Truvada) has a mild suppressive effect on weight and cholesterol. Because Descovy lacks this suppressive brake, people taking it or switching from Truvada typically gain around 1kg per year, which is the normal rate seen in the general population, along with a small increase in cholesterol.

What to do if you have side effects

If you ever experience side effects, speak with your doctor. Simple adjustments, like switching pills or timing your doses with meals, can keep you protected and feeling good.