Dutasteride 0.5 mg and CYP3A4 inhibitors (some antifungals, antibiotics, HIV medicines, verapamil, diltiazem)
CAUTION
CAUTION: the Avodart SmPC warns that long-term use of dutasteride with potent CYP3A4 inhibitors 'may increase serum concentrations of dutasteride', and that verapamil and diltiazem raised levels 1.6 to 1.8 times in studies. Tell your prescriber about any new long-term medicine.
Mechanism
Dutasteride is broken down in the liver mainly by the enzyme CYP3A4. Medicines that block CYP3A4 slow that breakdown, so dutasteride builds up to higher levels than usual. The Avodart SmPC names potent inhibitors 'e.g. ritonavir, indinavir, nefazodone, itraconazole, ketoconazole administered orally', and reports that the moderate inhibitors verapamil and diltiazem increased dutasteride concentrations 1.6 to 1.8 times.
The BNF's current list adds other medicines predicted to raise dutasteride exposure, including clarithromycin, erythromycin, fluconazole, posaconazole, voriconazole, cobicistat and several other HIV and cancer medicines. It rates these interactions mild to moderate, with the advice to monitor for side effects and adjust the dose where needed.
The timing matters. Dutasteride has a half-life of about 3 to 5 weeks, and the SmPC notes that with enzyme inhibition this may be prolonged further: 'it can take more than 6 months of concurrent therapy before a new steady state is reached'. A short course, such as a week of an antifungal, is a different situation from months of combined use, which is why the SmPC refers to long-term combination. For finasteride, its SmPC states that any increase from CYP3A4 inhibitors is unlikely to be clinically significant.
Practical advice
Tell your prescriber if you take, or are about to start long term, any antifungal tablet, macrolide antibiotic, HIV medicine, verapamil or diltiazem, or any other medicine your pharmacist flags as a CYP3A4 inhibitor. Tell the other prescriber that you take dutasteride for hair loss, off-label (see is dutasteride licensed for hair loss?).
Do not stop a needed medicine to protect your hair treatment. Most of these medicines treat something more important, and the SmPC approach is to manage the combination, not to avoid it at all costs: 'a reduction of the dutasteride dosing frequency can be considered if side effects are noted.' That decision belongs to your prescriber.
Watch for side effects while on both, particularly the sexual side effects listed for dutasteride (see dutasteride and sexual side effects). The MHRA Drug Safety Update of 11 May 2026 added a precautionary warning for dutasteride, because mood changes have been reported with finasteride; data for dutasteride were very limited. The Avodart SmPC notes sexual side effects may persist after stopping, with dutasteride's role unknown. Seek help promptly for low mood or suicidal thoughts; Samaritans are on 116 123 (free, 24/7).
More on dutasteride 0.5 mg, the MHRA safety updates and stopping dutasteride.