Tenofovir: What it does and why people take it

Tenofovir is a common antiviral you’ll see in HIV treatment, HIV prevention (PrEP), and hepatitis B care. It comes in two main forms — tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF). Both block the virus from copying itself, but they act a bit differently in the body, which affects safety and side effects.

How to take Tenofovir

Typical adult dosing is concrete: TDF is usually 300 mg once daily when used for HIV or hepatitis B. TAF is given at lower milligrams (commonly 25 mg once daily) because it gets into cells more efficiently — but TAF is almost always part of a combo pill, not taken alone. For PrEP, the standard is a fixed combo of TDF/FTC (300/200 mg) once a day. Some men who have sex with men use an event-driven 2-1-1 approach with TDF/FTC (two pills 2–24 hours before sex, one pill 24 hours after, and a third 48 hours after the first dose) — that’s recommended in some guidelines but not for everyone, so check with your clinician before trying it.

Take Tenofovir with or without food depending on the product instructions (some combinations advise with food). Don’t skip doses if you want protection from HIV — missed doses reduce effectiveness fast.

Safety checks and practical monitoring

Tenofovir works well, but it needs simple lab checks. Before starting, clinicians usually check kidney function (serum creatinine and eGFR), hepatitis B status, and an HIV test if using PrEP. With TDF, repeat kidney and phosphate checks are common — often at 3 months, then every 6–12 months. TDF can lower bone mineral density, so people with osteoporosis or risk factors may need a different option or bone scans. TAF tends to have less impact on kidneys and bones but can raise cholesterol and cause weight gain in some people.

Tell your provider about other meds. Tenofovir has important interactions: avoid using it with didanosine, and some boosted HIV regimens change drug levels. Also mention supplements and heavy use of NSAIDs if you have kidney risks.

Common side effects are mild — nausea, upset stomach, or headache. Serious issues are uncommon but include kidney problems and bone density loss. If you notice swelling, sudden fatigue, muscle pain, or unusual bone pain, contact your clinic.

Practical tips: store pills in a dry place, keep appointment labs, and carry a short list of your meds to every visit. If you buy meds online, use a licensed pharmacy that requires a prescription — cheap pills from unknown sellers can be fake or unsafe.

Want help reading your lab results or comparing TDF vs TAF for your situation? Ask your clinician — they’ll match the drug choice to your kidney health, bone risk, and what else you’re taking. Tenofovir is powerful and usually straightforward when monitored properly.