References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Efavirenz is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that was one of the most commonly prescribed HIV drugs worldwide for over 15 years. While newer alternatives are now preferred in most UK guidelines, efavirenz remains widely used globally and some UK patients continue on it successfully. This guide covers the key details.
For a broader overview of efavirenz including switching options, see our efavirenz overview.
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Dosing and Administration
| Detail | Guidance |
|---|---|
| Dose | 600mg once daily (or 400mg in some settings) |
| Timing | At bedtime on an empty stomach |
| Why bedtime | Reduces the impact of dizziness and vivid dreams |
| Why empty stomach | Food increases absorption and may worsen side effects |
Available Combinations
- Atripla — efavirenz + emtricitabine + tenofovir DF (single tablet)
- Sustiva — efavirenz alone (used with other drugs)
Side Effect Profile
Efavirenz has a distinctive side effect profile compared to newer drugs:
Neuropsychiatric effects
- Vivid dreams and nightmares — very common, can persist
- Dizziness — usually settles in weeks
- Difficulty concentrating
- Depression and mood changes
- Anxiety
- Rarely, suicidal thoughts — contact your clinic immediately
Other side effects
- Rash — usually in the first few weeks, usually mild
- Raised cholesterol
- Gynaecomastia (breast enlargement) — rare
- False positive on some cannabinoid drug tests
Pregnancy
Efavirenz was historically avoided in the first trimester due to concerns about birth defects. More recent data has been reassuring, but most UK specialists prefer dolutegravir or atazanavir-based regimens in pregnancy. If you become pregnant while on efavirenz, talk to your HIV team — you don’t need to stop urgently.
Resistance
Efavirenz has a low genetic barrier to resistance — a single mutation (K103N) can make it ineffective. This mutation also causes cross-resistance to nevirapine. If resistance develops, etravirine may still work depending on the specific mutation pattern.
Should You Switch?
If you’re well and tolerating efavirenz without problems, there’s no urgent reason to switch. But if you’re experiencing sleep disturbance, mood changes, or concentration problems, modern alternatives (dolutegravir, bictegravir) are better tolerated and your clinic can arrange the switch.
Read more: Efavirenz overview | Biktarvy | What is HIV?
Frequently Asked Questions
Can I take efavirenz with food?
It’s recommended on an empty stomach because food increases absorption and can worsen CNS side effects. Take it at bedtime, at least 2 hours after eating.
Will the dizziness go away?
Usually within 2-4 weeks. If it persists beyond a month, discuss switching with your clinic.
Is the 400mg dose as effective as 600mg?
Studies suggest the lower dose is effective in many patients with fewer side effects. Some UK clinics offer this option.
Related reading
- Efavirenz for HIV: An Older NNRTI Still in Use
- Eviplera: How This Anti-HIV Drug Works
- Dolutegravir: A Complete Guide to This HIV Medication
- Understanding Efavirenz in HIV Treatment
- Injectable HIV Treatment: Everything You Need to Know
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
