PrEP side effects: what is normal, how long they last, and when to see a doctor

Most people take PrEP without any side effects. Some notice mild stomach upset or a headache in the first few weeks, which usually settles on its own. Rarer effects on the kidneys and bones are the reason for regular check-ups.

In short: early side effects (nausea, headache, diarrhoea, tiredness) usually go within a few weeks. Taking the tablet with food or at bedtime helps. Don’t stop PrEP on your own, especially if you have hepatitis B: talk to the doctor first.

Common side effects (first few weeks)

• nausea or a mild upset stomach
• diarrhoea or loose stools
• headache
• tiredness
• bloating or wind

This is sometimes called “start-up syndrome”. It usually improves within the first month as your body gets used to the medicine.

Tips to ease them

• Take the tablet with food, or at bedtime so you sleep through any nausea.
• Take it at the same time every day.
• Drink enough water.
• For a headache, paracetamol is fine. Avoid regular anti-inflammatory painkillers (ibuprofen, diclofenac), which can strain the kidneys.

Less common: kidneys

Tenofovir can affect kidney function in a small number of people, usually mildly, and it typically improves when PrEP is stopped. That is why your kidney function is checked before you start and at least once a year. The risk is higher if you are older, have diabetes or high blood pressure, or take other medicines that affect the kidneys. Tell the doctor about all the medicines and supplements you take, including bodybuilding supplements.

Less common: bone density

Tenofovir can cause a small drop in bone mineral density, which usually recovers after stopping. It rarely causes problems in healthy adults. Weight-bearing exercise and enough calcium and vitamin D help keep bones strong. Tell the doctor if you have had fractures or have osteoporosis.

When to contact a doctor

• side effects that don’t settle after a month, or stop you taking PrEP
• fever, sore throat, rash or swollen glands (these can be signs of a new HIV infection, so you need an HIV test)
• passing much less urine, or swelling of the legs
• yellow skin or eyes, or dark urine

Thinking of stopping?

Talk to the doctor first. They will tell you how long to keep taking it after your last possible exposure. If you have hepatitis B, stopping suddenly can make it flare up.

Our doctors review every PrEP order and are on WhatsApp if side effects worry you. More in the guide to PrEP in Malaysia.