The short answer
The two main types of BPH medicine work in different ways and have different side effects. Alpha blockers such as tamsulosin relax the muscle around the urethra and often help within days. Their most common side effects are dizziness and changes in ejaculation. 5-alpha reductase inhibitors (finasteride, dutasteride) slowly shrink the prostate over months. A small share of men get sexual side effects, and they lower your PSA reading, which your doctor needs to know.
Most men tolerate these medicines well, and they are the most-studied treatments for BPH. Knowing what to expect helps you have a better conversation with your doctor, which is exactly what the American Urological Association's 2026 guideline asks for.
This article is for general education and is not medical advice. Never stop or change a prescribed medicine without talking to your doctor or pharmacist first.
At a glance: the main BPH medicines
| Medicine type | Examples | How it works | How fast | Side effects to know |
|---|---|---|---|---|
| Alpha blockers | Tamsulosin (Flomax), silodosin, alfuzosin, doxazosin, terazosin | Relaxes muscle in the prostate and bladder neck | Days to a few weeks | Dizziness, low blood pressure on standing, reduced or absent ejaculation, stuffy nose |
| 5-alpha reductase inhibitors (5-ARIs) | Finasteride (Proscar), dutasteride (Avodart) | Blocks DHT, shrinking the prostate by about 20–25% | 3–6 months | Lower libido, erection or ejaculation changes, breast tenderness; halves PSA |
| PDE5 inhibitor | Tadalafil 5 mg daily (Cialis) | Relaxes smooth muscle; also treats erectile dysfunction | A few weeks | Headache, indigestion, back pain; never with nitrate heart medicines |
| Combination therapy | Alpha blocker + 5-ARI (e.g. Jalyn), or tadalafil + alpha blocker or finasteride | Quick relief plus long-term shrinkage | Days, then months | The side effects of both medicines |
Alpha blockers (tamsulosin and others)
Alpha blockers are usually the first prescription men are offered. They don't shrink the prostate. Instead they relax the muscle around the urethra so urine flows more easily, which is why many men notice a stronger stream within days.
Ejaculation changes. This is the side effect men are least often warned about. Some men produce little or no semen at orgasm, because the muscles that move semen forward are also relaxed. A 2022 review of 75 randomized trials found alpha blockers raised the odds of ejaculatory problems in men with BPH about 7.5-fold compared with placebo. Silodosin carried about 3.5 times the odds of tamsulosin, while alfuzosin and the older non-selective drugs caused fewer problems. Importantly, the same review found no increase in erectile dysfunction. The effect is harmless and goes away if the medicine is stopped, but it can matter a great deal to men and couples.
Dizziness and low blood pressure. The older, non-selective drugs (doxazosin, terazosin) are more likely to cause light-headedness when you stand up, so they are usually started at a low dose at bedtime. Take care getting up at night, especially if you also take blood pressure medicines.
Tell your eye surgeon. If you're planning cataract surgery, tell your eye doctor if you have ever taken tamsulosin or another alpha blocker. These medicines can cause "floppy iris syndrome" during the operation. Surgeons can manage it well when they know in advance.
5-alpha reductase inhibitors (finasteride and dutasteride)
These are the only medicines proven to shrink the prostate. In the four-year PLESS trial, finasteride cut prostate volume by 18% while it grew 14% in men on placebo, and it roughly halved the risk of sudden urinary blockage or surgery. They work best in men with a larger prostate, generally over about 30 mL. If you're not sure what that means, see our guide to normal prostate size by age.
Sexual side effects. In large trials, a few percent more men on a 5-ARI than on placebo reported lower libido, erection problems or less semen. For most, these settle over time or after stopping. A small number of men report symptoms that persist, which is worth raising with your doctor before you start.
Your PSA will drop by about half. This matters. After 6 to 12 months on a 5-ARI, your PSA blood test reads roughly half its true value, so your doctor will usually double the result when checking for prostate cancer. Make sure anyone who orders a PSA test knows you're on one. Our guide to PSA results explains the test in more detail.
Health Canada warnings. In 2012, Health Canada advised that long-term use of finasteride or dutasteride may be linked to a small increase in the risk of high-grade prostate cancer, based on two large trials. It stressed that the risk is very small and that patients should not stop their medicine without speaking to their doctor. In 2015, Health Canada reviewed reports of mood changes with finasteride and found the evidence too limited to confirm a link with suicidal thoughts. Depression is already listed as a possible side effect. If you notice changes in mood, tell your doctor promptly.
Other effects. A small share of men notice breast tenderness or enlargement. Women who are or may be pregnant should not handle crushed or broken tablets.
Tadalafil and the new 2026 combinations
Daily low-dose tadalafil (5 mg), better known as an erectile dysfunction treatment, also eases urinary symptoms. The AUA's May 2026 guideline update now supports combining it with an alpha blocker, partly to help protect ejaculatory function, or with finasteride. Common side effects are headache, indigestion and back pain. Tadalafil must never be taken with nitrate heart medicines such as nitroglycerin, because together they can cause a dangerous drop in blood pressure.
Combination therapy
For men with a larger prostate and bothersome symptoms, doctors often combine an alpha blocker for quick relief with a 5-ARI for long-term shrinkage. In the landmark MTOPS trial, the combination reduced the risk of BPH getting worse more than either medicine alone. The trade-off is that you can get the side effects of both, so it's worth asking whether the alpha blocker can be stopped once the 5-ARI has had time to work.
Questions to ask your doctor
- Which medicine suits my prostate size and my main symptoms?
- How soon should I expect to notice a difference, and when will we review it?
- Will this affect ejaculation or sex, and is there an alternative if it does?
- Does it interact with my blood pressure, heart or other medicines?
- If I start a 5-ARI, how will my PSA results be interpreted?
- Is there a point where we would consider a procedure instead?
Before your appointment, it helps to score your symptoms with our free IPSS calculator, then repeat it after a few months on treatment.
What about lifestyle changes and supplements?
Lifestyle changes such as timing your fluids, cutting evening caffeine and alcohol, and staying active are recommended for every man with BPH, whether or not he takes medicine. We cover the evidence in can an enlarged prostate shrink naturally?
Some men with mild to moderate symptoms also try a Health Canada-licensed natural health product. Complete Prostate Health (NPN 80087894) is licensed to help relieve urinary symptoms of BPH. Supplements are not a replacement for a medicine your doctor has prescribed. If you take one alongside prescription treatment, tell your doctor and pharmacist.
Frequently asked questions
What is the most common side effect of tamsulosin?
Dizziness and changes in ejaculation, such as little or no semen, are the most common. Tamsulosin does not increase the risk of erectile dysfunction.
Do finasteride side effects go away?
For most men, sexual side effects ease over time or after stopping. A small number report effects that persist. Talk to your doctor before starting or stopping.
How long does finasteride take to work for BPH?
Usually 3 to 6 months for symptoms to improve, and up to a year for the full shrinking effect.
Does finasteride affect PSA tests?
Yes. After 6 to 12 months it lowers PSA by about half, so doctors usually double the result when screening for prostate cancer.
Can I stop BPH medication on my own?
No. Speak to your doctor first. Symptoms can return, and some men are at risk of urinary blockage.
References
- Buchholz N, et al. Effect of alpha-adrenoceptor antagonists on sexual function: a systematic review and meta-analysis. Arch Ital Urol Androl. 2022. Article
- McConnell JD, et al. The effect of finasteride on the risk of acute urinary retention and the need for surgical treatment among men with BPH (PLESS). N Engl J Med. 1998;338:557–63. PubMed
- McConnell JD, et al. The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of BPH (MTOPS). N Engl J Med. 2003;349:2387–98. PubMed
- Health Canada. Finasteride (Proscar, Propecia) and dutasteride (Avodart, Jalyn) may increase the risk of high-grade prostate cancer. March 2012. Advisory
- Health Canada. Summary Safety Review: Finasteride — assessing the potential risk of suicidal thoughts and behaviour. 2015. Review
- Intraoperative floppy iris syndrome in patients treated with tamsulosin. Swissmedic safety notice. Notice
- American Urological Association. Management of lower urinary tract symptoms attributed to BPH: AUA Guideline (2026). AUA announcement · AUA Daily News coverage
