Taking finasteride and dutasteride together is not recommended and offers no meaningful benefit over taking either drug alone. Both medications work by blocking the same enzyme system responsible for converting testosterone into DHT (dihydrotestosterone), the hormone that drives hair loss and prostate enlargement. Because dutasteride already covers everything finasteride does and more, combining them creates redundancy rather than added effect.
Why the Combination Is Redundant
Finasteride and dutasteride both belong to the same drug class: 5-alpha reductase inhibitors. The difference between them is scope. Finasteride selectively blocks only the type 2 form of the enzyme, while dutasteride blocks both type 1 and type 2 forms. This means dutasteride already does what finasteride does, plus more.
The numbers reflect this overlap clearly. Finasteride reduces DHT levels in the blood by up to 70% and in the prostate by over 90%. Dutasteride reduces DHT by up to 99% in both the blood and the prostate. Adding finasteride on top of dutasteride leaves almost nothing additional to block. You can’t suppress an enzyme that’s already 99% suppressed.
No published clinical trials have tested a combined regimen of both drugs taken simultaneously. This isn’t an oversight. Pharmacologically, there’s no rationale for the combination, so researchers haven’t pursued it. The two drugs compete for the same binding sites on the enzyme, meaning they would essentially crowd each other out rather than amplify the effect.
How the Two Drugs Compare Head to Head
For hair loss, both drugs are prescribed to lower DHT and slow or reverse miniaturization of hair follicles. Dutasteride achieves greater DHT suppression, and some studies suggest modestly better hair regrowth compared to finasteride. However, finasteride remains the more commonly prescribed option for hair loss because it’s been studied longer for that purpose and carries a slightly lower side effect burden for some patients.
For benign prostatic hyperplasia (BPH), a large comparison study of nearly 7,000 men found no statistically significant difference between dutasteride and finasteride when each was paired with an alpha blocker. Rates of acute urinary retention, prostate-related surgery, and overall disease progression were similar between the two groups after adjusting for patient differences. In practical terms, switching from one to the other doesn’t offer a dramatic improvement for most men with enlarged prostates, and stacking them wouldn’t change that picture.
The Half-Life Factor
One important difference between these drugs is how long they stay active in your body. Finasteride has a half-life of 6 to 8 hours, meaning it clears relatively quickly. Dutasteride has a half-life of roughly 5 weeks, which means it builds up in your system over months and lingers long after you stop taking it.
This matters if you’re thinking about combining them or switching between them. If you’ve been taking dutasteride, it will remain active in your body for several months after your last dose. Adding finasteride during that window would be especially pointless, since dutasteride is still occupying those enzyme binding sites. Conversely, if you’re switching from finasteride to dutasteride, the transition is straightforward because finasteride clears within a day or two.
Side Effects Don’t Cancel Out
Both drugs share the same core side effects: reduced libido, erectile difficulties, and decreased ejaculate volume. These occur because lowering DHT affects androgen signaling throughout the body, not just in the scalp or prostate. Taking both drugs together would not reduce these risks. If anything, the deeper DHT suppression from combining them could increase the likelihood or severity of sexual side effects without delivering a therapeutic benefit you couldn’t already get from dutasteride alone.
Both drugs also suppress prostate-specific antigen (PSA) levels by approximately 50%. Doctors typically double a PSA reading for patients on either drug to get an accurate estimate. If you were taking both, the PSA suppression effect wouldn’t meaningfully change, but the situation could create confusion during prostate cancer screening if your provider isn’t aware of your full medication list.
What to Do if One Drug Isn’t Working
If you’re on finasteride and not seeing results, the logical next step is switching to dutasteride rather than adding it on top. Since dutasteride blocks both enzyme types and achieves near-complete DHT suppression, it represents a genuine escalation in treatment. Most prescribers will recommend trying one drug for at least 6 to 12 months before concluding it isn’t effective, since hair regrowth and prostate changes take time to manifest.
If dutasteride alone isn’t producing the results you want for hair loss, the more productive approach is adding a treatment from a different drug class, such as a topical vasodilator, rather than layering on another drug that hits the same target. For BPH, combining a 5-alpha reductase inhibitor with an alpha blocker (a drug that relaxes prostate and bladder neck muscles) is a well-studied strategy that addresses two different mechanisms of the disease.
The bottom line: finasteride and dutasteride are variations on the same theme, not complementary tools. Using both at once doubles your pill count without doubling the benefit.