Like all medicines, PrEP can cause side some effects.
This 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.
Sometimes people have more serious side effects. But this is not common.
Reduced kidney function
A small number of people taking PrEP develop reduced kidney function. This is why you have your kidneys checked before starting.
Kidney function usually goes back to normal when you stop taking PrEP.
The risk of kidney problems is higher if you:
- 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 loss reverses after you stop taking PrEP.
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
Taking PrEP with other medicines
PrEP medicines tenofovir and emtricitabine do not usually interact with other medicines.
Interaction means that when certain medicines are taken together, you may develop problems or side effects.
If you take tenofovir with non-steroidal anti-inflammatory drugs (NSAIDs), especially diclofenac, it can cause kidney problems. Other medicines in this class include ibuprofen and naproxen. Avoid NSAIDs if you are taking PrEP, or tell your healthcare professional if you need to take them.
Always 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 them hard to interpret.
You can also ask a pharmacist before starting medicines. This includes medicines you buy without a prescription. Tell them you are taking PrEP so that 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.
But some studies show slightly lower levels of PrEP medicine in transgender women taking feminising hormones. Transgender women who take 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.
