Efavirenz is commonly taken in the evening because CNS side effects, such as vivid dreams, often diminish when the drug is taken before sleep. If insomnia persists, discuss timing adjustments or alternative regimens with your prescriber.
Efavirenz is not a controlled substance and is not screened for in standard workplace drug tests. However, some occupational health programs may request a medication list; disclose efavirenz to avoid misunderstandings.
In the UK, 600 mg efavirenz tablets typically carry the imprint “EFA 600” while 200 mg tablets may be imprinted “EFA 200”. Imprints help verify authenticity when pharmacy staff check the medication.
Efavirenz has a long half-life, allowing once-daily dosing, which is convenient for travel. Carry a sufficient supply, keep tablets in original packaging, and have a copy of your prescription in case you need to refill abroad.
Both drugs inhibit reverse transcriptase, but efavirenz generally has a higher genetic barrier to resistance and is once-daily, whereas nevirapine is dosed twice daily and has a higher risk of hepatotoxicity in certain populations. Choice depends on individual clinical factors.
Efavirenz can reduce plasma concentrations of some hormonal contraceptives (e.g., levonorgestrel) by inducing CYP enzymes, potentially decreasing contraceptive effectiveness. Using a non-hormonal method or a higher-dose contraceptive may be advised.
Keep the medication in a cool, dry place away from direct sunlight. If you expect extreme temperatures, store the tablets in a sealed bag with a desiccant packet and avoid leaving them in a car.
Efavirenz is available as a generic medication, which can be prescribed through the NHS at a lower cost than brand-name products. Discuss generic options with your prescriber to optimise affordability.
Antacids containing aluminium or magnesium do not significantly affect efavirenz absorption. However, high-dose calcium or iron supplements may modestly reduce plasma levels; spacing them several hours apart is prudent.
Efavirenz’s original patents have expired, allowing multiple manufacturers to produce generic versions. This facilitates broader access and competitive pricing.
Efavirenz is an antiretroviral medication classified as a non-nucleoside reverse transcriptase inhibitor (NNRTI). It is prescribed for the management of HIV-1 infection and is available in oral pill form in strengths of 200 mg and 600 mg. In the United Kingdom the drug is prescription-only (POM) and regulated by the Medicines and Healthcare products Regulatory Agency (MHRA).
Efavirenz binds directly to the reverse transcriptase enzyme of HIV-1, blocking the enzyme’s ability to copy viral RNA into DNA. This inhibition stops the virus from replicating inside host cells. The drug is well absorbed after oral administration, reaches peak plasma concentrations in about 3-5 hours, and has a long half-life of 40-55 hours, allowing once-daily dosing. Efavirenz is metabolised mainly by the liver enzyme CYP2B6 and, to a lesser extent, by CYP3A4.
Efavirenz is typically combined with two nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) such as tenofovir disoproxil fumarate and emtricitabine, forming a complete treatment regimen.
Evidence-Based Off-Label Uses
Off-label use requires medical supervision and individualized risk assessment.
Special populations such as the elderly or patients with renal impairment usually do not require dose changes, but clinicians may monitor drug levels in patients with known CYP2B6 polymorphisms.
Major interactions
Ritonavir, cobicistat, or other strong CYP3A4 inhibitors increase efavirenz concentrations; dose reduction may be necessary.
Carbamazepine, phenobarbital, rifampicin, or St. John’s wort (CYP2B6 inducers) lower efavirenz levels, potentially reducing efficacy.
Moderate interactions
Protease inhibitors (e.g., atazanavir, lopinavir/ritonavir) can raise efavirenz levels; monitoring for CNS toxicity is advised.
Warfarin: Efavirenz may reduce warfarin anticoagulant effect; INR should be checked regularly.
This article provides educational information about efavirenz and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.
