If your doctor has brought up dutasteride vs finasteride for an enlarged prostate, you’re probably trying to figure out one thing: which one will actually make the symptoms ease up faster, and which one will give you fewer problems while doing it.
Both drugs belong to the same class, called 5-alpha reductase inhibitors (5-ARIs). They both shrink the prostate by lowering dihydrotestosterone (DHT), the hormone that drives prostate growth. But they don’t work in identical ways, and the differences matter more than most patients realize when they leave the clinic with a new prescription.
What I tell patients is this: the textbook answer favors dutasteride for raw shrinkage speed and degree. The honest answer is more nuanced, because side effects, cost, and how bothered you are by your symptoms all factor in. Here’s how the two actually compare.
How Each Drug Works
Finasteride blocks only one form of the 5-alpha reductase enzyme (type 2). Dutasteride blocks both type 1 and type 2. That’s the core mechanistic difference, and it’s why dutasteride suppresses DHT more completely, roughly 90 to 95 percent reduction versus about 70 percent with finasteride, according to data summarized by the National Institutes of Health.
More DHT suppression usually means more prostate shrinkage. That’s the theory. In practice, the gap is smaller than the lab numbers suggest, because the prostate doesn’t need 95 percent DHT suppression to shrink meaningfully. Once you knock DHT down past a certain threshold, the prostate responds.
Both are FDA-approved for benign prostatic hyperplasia (BPH). Finasteride at 5 mg is sold as Proscar, and dutasteride at 0.5 mg is sold as Avodart. Your prescriber will determine the right dose for your situation.
Dutasteride vs Finasteride: Which Shrinks the Prostate Faster?
Head-to-head data here is limited but consistent. The EPICS trial, published in European Urology in 2011, ran a 12-month comparison and found dutasteride and finasteride produced similar prostate volume reductions, roughly 25 to 27 percent, by the one-year mark. Symptom scores improved comparably too.
Where dutasteride seems to edge ahead is in the first several months. Because it suppresses DHT more completely and more quickly, some patients notice symptom relief sooner, often around the 3 to 6 month window rather than 6 to 12 months. But "sooner" is measured in weeks, not days. Neither drug works fast.
A few specifics worth knowing in the dutasteride vs finasteride comparison:
- Both typically take 3 to 6 months before patients notice meaningful symptom improvement.
- Maximum prostate shrinkage usually shows up around 12 to 24 months.
- Both lower PSA values by roughly 50 percent, which your urologist needs to know when interpreting prostate cancer screening results.
- The CombAT study showed dutasteride combined with tamsulosin reduced BPH progression more than either drug alone.
If raw speed of shrinkage is your priority and you have a large prostate (over 40 mL), dutasteride is often the first pick. For moderately enlarged prostates, the dutasteride vs finasteride choice often comes down to side effects and cost rather than efficacy.
Side Effect Comparison
This is where the conversation gets honest. Both drugs share the same side effect profile, mostly sexual, and the rates are close but not identical.
The Mayo Clinic lists the common side effects for both as decreased libido, erectile dysfunction, ejaculation problems, and breast tenderness or enlargement (gynecomastia). In clinical trials:
- Decreased libido: about 3 to 6 percent on finasteride, 3 to 7 percent on dutasteride
- Erectile dysfunction: 5 to 8 percent on both
- Ejaculation disorders: slightly higher on dutasteride, around 1 to 2 percent versus under 1 percent
- Gynecomastia: 1 to 2 percent on both
Most patients tolerate either drug fine. A small subset, though, experience persistent sexual side effects that don’t go away after stopping, sometimes called post-finasteride syndrome. The evidence on how common this actually is remains debated, but it’s real enough that you should know the warning signs. We covered this in detail in our piece on finasteride side effects and when to stop treatment.
Dutasteride has a longer half-life (about 5 weeks versus 6 to 8 hours for finasteride), which means if side effects hit, they take longer to wash out. That’s a practical consideration if you’re someone who likes the option to stop quickly.
Cost and Practical Considerations
Generic finasteride is dirt cheap now, often under 15 dollars a month at most US pharmacies. Generic dutasteride has come down significantly too, usually in the 20 to 40 dollar range monthly. Brand-name Avodart still runs over 200 dollars without insurance. Compare prices on generic finasteride and dutasteride at edrugstore.com to see what fits your budget.
For most insurance plans, finasteride is preferred on the formulary. Dutasteride often requires a step-therapy trial of finasteride first unless your urologist documents a reason to skip ahead.
If your symptoms are predominantly urinary urgency and weak stream rather than significant prostate enlargement, an alpha blocker may be more appropriate than a 5-ARI. Our comparison of tamsulosin versus alfuzosin for BPH walks through that decision. And if you’re already on a 5-ARI and worried about combining it with ED medication, our overview of tadalafil with blood pressure meds covers the interactions you should flag with your prescriber.
So Which One Should You Take?
For most men with moderately enlarged prostates and bothersome symptoms, finasteride is the reasonable starting point. It’s cheaper, well-studied, and effective. For men with significantly enlarged prostates (over 40 mL), faster symptom relief preferences, or who didn’t respond well to finasteride after 6 months, dutasteride is a defensible second choice.
The dutasteride vs finasteride debate doesn’t have one winner. It has one right answer for your specific prostate size, symptom severity, side effect tolerance, and budget. Bring those four pieces of information to your urologist appointment and the choice gets a lot easier.
Ask your pharmacist whether your insurance covers dutasteride directly or requires a finasteride trial first, and talk to your doctor about getting your prostate volume measured before starting either drug. That single number changes the dutasteride vs finasteride math more than anything else.
This article is for informational purposes only and is not medical advice. Always consult a licensed pharmacist or physician before starting, stopping, or changing any medication.
References
- National Institutes of Health, 5-Alpha Reductase Inhibitors, mechanism and DHT suppression data for both drugs.
- FDA Drugs Database, regulatory approval and labeling information for finasteride and dutasteride.
- Mayo Clinic, Finasteride, patient-facing side effect and dosing reference.
Dr Steven Schlosser
Dr. Schlosser graduated from Lafayette College Phi Beta Kappa and attended Georgetown Medical School. He had 4 years of medical residency training at Tufts University in Boston in both Gynecology and Internal Medicine. He has had a spotless medical career for the past 40+ years and is Board Certified. Learn More