Finasteride and Tamsulosin Together: Why, and for How Long

Yes, finasteride and tamsulosin can be taken together, and very often are. They are prescribed as a pair because they do two different jobs for an enlarged prostate, on two very different timescales. Proscar and Flomax, the brand names, are the same combination.

Why they are prescribed together

Tamsulosin is an alpha blocker. It relaxes the muscle in the prostate and at the neck of the bladder, so urine flows more easily. It works within days. It does not change the size of the prostate or the course of the condition, and its effect disappears within a day or two of stopping.

Finasteride is a 5-alpha-reductase inhibitor. It blocks the conversion of testosterone to the hormone that drives prostate growth, and over six to twelve months the prostate shrinks, typically by around a fifth. It does almost nothing for symptoms in the first months. What it does, and tamsulosin does not, is lower the long-term risk of the bladder blocking completely and of needing an operation.

So the combination gives fast relief from one drug while the other slowly changes the underlying problem.

What the combination did in the trials

The Medical Therapy of Prostatic Symptoms trial followed 3,047 men for an average of four and a half years on placebo, doxazosin (an alpha blocker like tamsulosin), finasteride, or both. Against placebo, the risk of the condition progressing fell by 39 percent with doxazosin, 34 percent with finasteride and 66 percent with the combination, which was significantly better than either drug alone. Symptom scores also improved most with the combination.

The detail that matters most: only finasteride and the combination reduced the risk of acute urinary retention and of needing surgery. Doxazosin alone did not. Over the long run, the alpha blocker manages symptoms and the 5-alpha-reductase inhibitor is what protects against the serious outcomes.

The CombAT trial tested the same idea with dutasteride and tamsulosin in 4,844 men with an enlarged prostate over four years. The combination beat tamsulosin alone at preventing retention and surgery, but not dutasteride alone, which is the same pattern. It beat both at preventing overall progression and gave the largest symptom improvement. On night-time urination it also came out ahead, though the differences were small: on the 0 to 5 nocturia question of the symptom score, the combination improved by 0.5 points over four years, dutasteride by 0.4 and tamsulosin by 0.3.

Who the combination is for

Men with moderate to severe symptoms and a prostate that is actually enlarged. The trials enrolled men with prostates of at least 30 ml, and finasteride does little for a prostate that is not enlarged, because there is little extra tissue for it to shrink. If your prostate is normal-sized and your problem is mostly symptoms, an alpha blocker on its own is usually the more sensible choice.

Prostate size is estimated from a rectal examination or an ultrasound, and PSA is a rough guide, since it rises with prostate volume.

How to take them

Tamsulosin is usually taken once a day, about 30 minutes after the same meal each day, often the evening meal because it can cause dizziness on standing. Finasteride is taken once a day with or without food. There is no known interaction that changes how either drug works, so they can be taken at the same time if that is easier to remember.

Expect the stream to improve within a week from the tamsulosin. Expect nothing obvious from the finasteride for months. The temptation is to stop it because nothing seems to be happening, which is exactly when it is doing its work.

Side effects of taking both

The side effects add up rather than interact. From tamsulosin: dizziness on standing, a stuffy nose, and reduced or absent ejaculation. From finasteride: reduced libido, erectile difficulty and reduced ejaculate volume in a minority of men. Taking both means a higher chance of some sexual side effect than taking either alone.

Two warnings are specific to finasteride. In 2011 the FDA added a warning that 5-alpha-reductase inhibitors may increase the risk of high-grade prostate cancer, based on two large prevention trials, even though they lowered the overall number of prostate cancers found. And mood changes, including depression, have been reported. Tell your doctor promptly if your mood changes.

And one that is specific to tamsulosin, which applies for life: tell any eye surgeon you have taken it before cataract surgery, because it can cause a complication called floppy iris syndrome.

Finasteride halves your PSA

This is the point most often missed. After six to twelve months, finasteride lowers PSA by roughly half. A PSA of 2.0 on finasteride corresponds to about 4.0 without it. Doctors usually double the reading to interpret it, but only if they know you take it.

Make sure whoever orders your PSA test knows about the finasteride. And because the drop is predictable, a PSA that fails to fall as expected, or starts rising while you are on finasteride, deserves attention rather than reassurance.

Do you have to take both forever?

Often not. The trials point to the alpha blocker as the one that can usually be dropped once the finasteride has had time to work.

In the SMART-1 trial, men took dutasteride and tamsulosin together for 24 weeks, then some stopped the tamsulosin. Six weeks later, 77 percent felt the same or better than before stopping. Among men whose symptoms were not severe, 84 percent made the switch without a noticeable change. Men with severe symptoms did worse: 42.5 percent of them felt their symptoms worsen after stopping, against 14 percent of men who stayed on both.

A 2023 study of men who had been on combination therapy for at least a year and then dropped one drug found the same direction. Those who stopped the alpha blocker did better than those who stopped the 5-alpha-reductase inhibitor: 6.1 percent needed prostate surgery against 14.3 percent, and 23 percent went back on both drugs against 38.9 percent.

So if you want to be on fewer drugs, the one to ask about stopping is usually tamsulosin, after six to twelve months, and only if your symptoms were moderate rather than severe to begin with. Stopping finasteride instead lets the prostate regrow and loses the protection against retention and surgery.

Can you take finasteride for hair loss with tamsulosin?

Yes. Hair-loss finasteride is the same drug at 1 mg a day rather than the 5 mg used for the prostate. It still lowers PSA, so the same rule about telling whoever orders your PSA test applies. It is not a substitute for the prostate dose: the prostate trials used 5 mg.

Questions to ask your doctor

How big is my prostate, and is it large enough for finasteride to help? When should we review whether I still need the tamsulosin? What PSA should I expect on finasteride, and who will interpret it? And if sexual side effects appear, would a different alpha blocker, such as alfuzosin, reduce them?