Like all medicines, PrEP can cause side effects.
These may include:
- mild nausea
- diarrhoea
- bloating
- headache
Fewer than 1 in 10 people taking PrEP have these side effects. They usually stop within the first month.
More serious side effects
You can have more serious side effects. But these are not common.
Reduced kidney function
PrEP can affect how well your kidneys work. This is why your kidneys are checked before you start PrEP.
If your kidney function is affected by PrEP, your doctor or nurse will talk to you about what to do.
You may be at higher risk of kidney problems if you:
- are age 40 or older
- already have reduced kidney function before starting PrEP
- are taking other medicine that can affect your kidney function
Reduced bone density
PrEP can reduce bone density by between 1% and 2%, causing slight thinning of the bones.
This side effect may be serious if you:
- already have low bone density for other reasons
- are under age 24 and your bones are still developing
Your doctor or nurse will talk to you more about your risk of reduced bone density on PrEP.
Taking PrEP with other medicines
You can develop problems or side effects when you take certain medicines together. This is called an interaction.
The PrEP medicines used in Ireland are tenofovir and emtricitabine. They do not usually interact with other medicines.
If you take tenofovir with non-steroidal anti-inflammatory drugs (NSAIDs), especially diclofenac, it can cause kidney problems. Other NSAIDs include ibuprofen and naproxen.
Avoid NSAIDs if you are taking PrEP, or tell your healthcare professional if you need to take them.
Gym supplements
Tell your healthcare professional if you are prescribed other medicines or you take gym supplements. Gym supplements such as creatine may affect your kidney function test results. This can make the test results hard to interpret.
You can also ask a pharmacist if you are on PrEP and are starting new medicines. This includes medicines you buy without a prescription. They can check for any likely interactions.
Hormone therapy
If you are taking PrEP along with gender-affirming hormones, there is no reason to expect PrEP will affect the hormone therapy.
Transgender women who take feminising hormone therapy should use daily PrEP. This is because studies show slightly lower levels of PrEP in people taking these hormones.
They should only use event-based dosing while under the care and supervision of a consultant in sexual health or infectious diseases.