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Pharmacology · Non-nucleoside reverse transcriptase inhibitors (NNRTIs)

Efavirenz !

A once-daily NNRTI used for years as first-line treatment. Typical effects are dizziness, vivid dreams and psychiatric symptoms.

Updated 2026-11-01

Also called: EFV

The figure shows efavirenz in the allosteric pocket of HIV-1 reverse transcriptase.

Target in 3D: HIV-1 reverse transcriptase (NNRTI pocket). PDB structure 1FK9 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

It binds the hydrophobic pocket of the p66 subunit of HIV-1 reverse transcriptase, away from the active site, leaving the enzyme stiff and twisted so it stops copying viral RNA into DNA. It needs no phosphorylation. A single mutation (such as K103N) is enough to lose its effect.

  1. It binds the allosteric pocket of reverse transcriptase
  2. It distorts the enzyme without competing with nucleotides
  3. Copying of viral RNA into DNA stops

Pharmacokinetics

Metabolism
Liver, mainly by CYP2B6; it induces CYP3A and CYP2B6, including its own clearance
Half-life
Long: about 40 to 55 hours at steady state

Indications

Adverse effects

Common

  • Dizziness, insomnia, vivid dreams, poor concentration (usually settle within weeks)
  • Rash in the first weeks
  • Raised lipids

Contraindications

  • Previous severe hypersensitivity (Stevens-Johnson, erythema multiforme)
  • Use with elbasvir/grazoprevir

Key interactions

Drugs metabolised by CYP3A or CYP2B6
Efavirenz induces these enzymes and can lower their levels
Hormonal contraceptives
They can lose efficacy: a barrier method is added
Voriconazole
Two-way interaction requiring adjustment of both drugs

What is monitored

  • Mood and psychiatric symptoms
  • Liver tests
  • Lipids
  • Pregnancy test before starting in women of childbearing potential

Administration and safety

  • By mouth, on an empty stomach and preferably at bedtime, to tolerate nervous system symptoms better
  • It can give a false positive on some urine cannabinoid tests

Nursing care

  • Warn that dizziness and vivid dreams are common at first and usually settle
  • Ask about depression or suicidal thoughts and refer at once
  • Teach to avoid hazardous tasks while dizzy
  • Advise added barrier contraception

Pregnancy and breastfeeding

There are retrospective reports of neural tube defects after first-trimester exposure; effective contraception is advised during treatment and for weeks afterwards because of its long half-life.

Test yourself

Think of the answer, then tap the question to see it.

What are efavirenz's most typical adverse effects?

Nervous system effects: dizziness, insomnia, vivid dreams and sometimes severe psychiatric symptoms.

Why is it given at bedtime?

So the nervous system symptoms, strongest after the dose, fall during sleep and are better tolerated.

What does efavirenz do to hormonal contraceptives?

By inducing cytochrome enzymes it can reduce their efficacy; a barrier method is added.

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← Back to the class: Non-nucleoside reverse transcriptase inhibitors (NNRTIs)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - EFAVIRENZ tablet, film coated (DailyMed (U.S. National Library of Medicine), 2024); Efavirenz: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); WHO recommends dolutegravir as preferred HIV treatment option in all populations (World Health Organization, 2019).

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Representative model, for educational purposes only.