Like all medicines, PrEP can cause side some effects.
This can include:
- mild nausea
- diarrhoea
- bloating
- headache
Less than 1 in 10 people taking PrEP experience these side effects and they usually stop within the first month.
Most people taking PrEP do not report any major side effects. Occasionally PrEP can cause more serious side effects.
Kidney function
Taking PrEP can affect your kidneys. This is is why monitoring your kidneys is very important. In the small number of people taking PrEP who develop reduced kidney function, these changes are usually reversed on stopping PrEP. This risk is higher if you are aged 40 years and over or if you already have reduced kidney function when you start PrEP.
Bone density
PrEP can also reduce bone density by between 1% and 2%, causing slight thinning of the bones. This loss reverses after PrEP is stopped. This side effect might be more important if you already have low bone density related to other factors. It might also be important if you are younger than 30 years as your bones are still developing.
PrEP and other medications
Tenofovir and emtricitabine do not interact with many other medicines. Interaction means that 2 or more drugs combined can cause problems or side effects.
One important consideration is between tenofovir and non-steroidal anti-inflammatory drugs (NSAIDs), especially diclofenac. Together these can cause kidney problems. Other medicines in this class include ibuprofen and naproxen. Avoid using these medicines if you are taking PrEP, or let your healthcare provider know if you need to take them.
You should always tell your healthcare provider (including your GP) if you are prescribed other medicines or taking gym supplements. You can also ask a pharmacist. Tell them you are taking PrEP so that they can check for any interactions. This includes over-the-counter medications.
Hormone therapy
For transgender people taking PrEP, there is no reason to expect PrEP will change the effectiveness of hormone therapy.
But some studies have shown slightly lower levels of PrEP in transgender women taking feminising hormones. Transgender women who are taking gender-affirming (feminising) hormone therapy can use daily PrEP. They should only use event-based dosing while under the care and supervision of a consultant in genitourinary medicine or infectious diseases.
