5-alpha-reductase inhibitor (type II)
Finasteride with the birth control pill
Many women of reproductive age take a combined or progestogen-only oral contraceptive while also using a chronic medication such as Finasteride (Finasteride). The combination is generally fine at 1mg, but a small number of medications can reduce contraceptive efficacy meaningfully and need either a backup method or a switch.
How Finasteride can affect contraceptive efficacy
Combined and progestogen-only contraceptives are metabolised through CYP3A4. Strong CYP3A4 inducers (some antiepileptics, rifampicin, St John's Wort) lower contraceptive plasma levels and reduce efficacy. Whether Finasteride acts on CYP3A4 determines whether Finasteride affects contraception. Most agents in 5-alpha-reductase inhibitor (type II) have no clinically meaningful effect on the pill at 1mg.
Practical guidance
According to the prescribing information for Finasteride, women on hormonal contraception should review Finasteride with the prescribing pharmacist or doctor. Where an interaction is documented, additional barrier contraception or switching to a non-oral method (IUD, implant) for the duration of Finasteride therapy is the standard mitigation.
Frequently asked questions
Will Finasteride make my pill less effective? ▾
Most 5-alpha-reductase inhibitor (type II) medications at 1mg do not affect oral contraceptive efficacy. The exceptions are CYP3A4-inducing drugs and a small number of others. The prescribing information for Finasteride states whether the interaction is meaningful.
Do I need a backup contraceptive on Finasteride? ▾
Backup contraception is needed only when there is a documented interaction between Finasteride and the contraceptive method. For most users at 1mg, no backup is required. The pharmacist confirms whether Finasteride interacts with hormonal contraception.
Products containing Finasteride
More on Finasteride
- With alcoholFinasteride and alcohol — is it safe to drink?
- With foodShould Finasteride be taken with food?
- Side effectsFinasteride side effects: common, rare and warning signs
- Dosage guideFinasteride dosage guide: how much to take and when
- OnsetHow fast does Finasteride start working?
- DurationHow long does Finasteride last?
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.