Prostate Health · Medicines
BPH Medicines Explained (Tamsulosin, Finasteride) and Their Sexual Side Effects
By OakMan Guide Editorial Team Updated 12 min read
The short answer
BPH medicines work in two ways: tamsulosin relaxes the muscle at the bladder neck so urine flows easier, and finasteride slowly shrinks the prostate. Sexual side effects can come with both, but they are not the rule. In the FDA label trials, ejaculation changes affected about 8 in 100 men on tamsulosin 0.4 mg, and finasteride's effects were concentrated in the first year. Your doctor wants to hear about them.
We're not doctors, and this is not medical advice. Everything below comes from the sources listed at the end, and any change to your medicine is a decision for you and your doctor.
If a doctor has put you on a BPH pill, or suggested one, the next question is usually the one nobody likes asking out loud. Here is what the official labels and health agencies actually say.
What are the main BPH medicines, and how do they work?
Two families do most of the work. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) describes them in one line each. Alpha blockers relax the muscles in the bladder neck and prostate, making it easier to urinate. 5-alpha reductase inhibitors (5-ARIs) help stop the growth of the prostate or help shrink it, improving urine flow.
The two names in this article's title are the best-known example of each:
- Tamsulosin (brand name Flomax) is an alpha blocker. MedlinePlus says it works by relaxing the muscles in the prostate and bladder so that urine can flow easily. It is a capsule taken once a day, 30 minutes after a meal.
- Finasteride (brand name Proscar) is a 5-ARI. MedlinePlus says it blocks the production of a male hormone that enlarges the prostate. Dutasteride (Avodart) belongs to the same family. The lower-dose finasteride sold as Propecia is used for hair loss, which is a separate use.
One more thing both pages say, and it is worth knowing before you start: these medicines control BPH, they do not cure it. They are meant to be taken for as long as your doctor advises, so the question of side effects is really a question about living with the medicine day to day.
How long do these medicines take to work?
This is where the two families differ. MedlinePlus says it may take at least 6 months before BPH symptoms improve on finasteride, because it works by changing the size of the gland. The MedlinePlus page on tamsulosin gives no such timeline, so ask your doctor what to expect from it and when. Neither page makes a promise, and neither should be read as one.
If your main trouble is the night trips, what is behind them and the free habits worth trying first are in why you wake up to pee at night, and the full list of signs is in enlarged prostate symptoms after 50.
What sexual side effects does tamsulosin cause?
The one that stands out is a change in ejaculation. The FDA-approved Flomax label reports it from two 13-week U.S. placebo-controlled trials in 1,487 men, and it says the effect was dose-related. Here is the table, with decreased libido and dizziness next to it:
| Side effect | Tamsulosin 0.4 mg | Tamsulosin 0.8 mg | Placebo |
|---|---|---|---|
| Abnormal ejaculation (includes decreased or no ejaculate and retrograde ejaculation) | 8.4% | 18.1% | 0.2% |
| Decreased libido | 1.0% | 2.0% | 1.2% |
| Dizziness | 15% | 17% | 10% |
So at the 0.4 mg strength, about 8 men in 100 noticed a change, against 2 in 1,000 on placebo. The number rose to 18% at double the dose, and only 8 of 492 men (1.6%) in that 0.8 mg group left the trials because of it. Nobody on the 0.4 mg capsule or on placebo did.
The NHS lists problems ejaculating as a common side effect (more than 1 in 100 people) and says that when semen volume is low or absent, you do not need to worry because this side effect is harmless. It adds that you should talk to a doctor if it bothers you or does not improve.
What is retrograde ejaculation?
It is the most likely reason behind a "dry" orgasm on an alpha blocker. MedlinePlus explains that semen goes backward into the bladder instead of out through the penis. The signs are little or no semen and, sometimes, cloudy urine afterward. MedlinePlus says it is usually not a problem unless you are trying to conceive, and that when a medicine is the cause, stopping it often restores normal ejaculation. If you are not trying for a child and it does not bother you, no treatment is needed.
What about erections? The label does not list erectile dysfunction among the common effects of tamsulosin. The one erection-related warning is rare: MedlinePlus lists a painful erection that lasts for hours as a serious side effect, and the NHS says to go to A&E if you get a painful erection that lasts 2 or more hours. The FDA label puts the chance at probably less than 1 in 50,000 men.
What sexual side effects does finasteride cause?
Three things can show up: less desire, trouble with erections, and a smaller amount of semen. The FDA Proscar label gives the numbers from PLESS, a 4-year placebo-controlled study with 1,524 men on finasteride and 1,516 on placebo. It lists only the effects the investigators judged possibly, probably or definitely related to the drug and that occurred in at least 1% of men on it.
| Side effect | Year 1, finasteride | Year 1, placebo | Years 2-4, finasteride | Years 2-4, placebo |
|---|---|---|---|---|
| Impotence | 8.1% | 3.7% | 5.1% | 5.1% |
| Decreased libido | 6.4% | 3.4% | 2.6% | 2.6% |
| Decreased volume of ejaculate | 3.7% | 0.8% | 1.5% | 0.5% |
| Ejaculation disorder | 0.8% | 0.1% | 0.2% | 0.1% |
Read the table from left to right. In year 1, impotence was 8.1% on finasteride and 3.7% on placebo, and decreased libido was 6.4% against 3.4%. By years 2 to 4, the label says there was no significant difference between the groups in impotence, decreased libido and ejaculation disorder: both groups sat at 5.1% for impotence and 2.6% for libido. The label's own wording is that there is no evidence of increased sexual adverse experiences with increased duration of treatment, and that new reports decreased with duration of therapy.
Treatment was stopped because of sexual-function side effects by 3.7% of men on finasteride and 2.1% on placebo. Put the other way, more than 96 men in 100 on finasteride did not stop for that reason.
If erection trouble is on your mind for any reason, our article on erectile dysfunction after 50 lists the other causes the NIDDK and Mayo Clinic name and when to bring it up with your doctor.
The label also reports a smaller amount of semen: in a 24-week study of healthy volunteers, the median drop in ejaculate volume was 0.6 mL (22.1%), with sperm concentration, motility and shape not meaningfully changed, and the label says these changes were reversible after stopping. The NHS lists problems getting an erection and less interest in sex as common side effects (more than 1 in 100 people), and says they usually improve after a while.
Can the side effects last after you stop?
This is the question behind many forum threads, so here is exactly what the official pages say. The FDA label lists sexual dysfunction that continued after stopping treatment, including erectile dysfunction, decreased libido and ejaculation disorders, among the postmarketing reports. It says these were reported rarely in men taking Proscar for BPH, that most of those men were older and were taking other medicines or had other conditions, and that the independent role of the medicine in those events is unknown. The NHS says the common side effects usually improve after a while, but they can sometimes carry on even after you stop taking finasteride.
The same two pages carry one more warning that matters more than anything above. The label lists depression and suicidal ideation in its postmarketing section, and MedlinePlus tells you to call your doctor for new or worsening depression or thoughts about harming or killing yourself. The NHS suggests telling family or friends you take finasteride so they can help you notice changes in mood. If you feel that way, call your doctor, or emergency services, the same day.
What happens when the two families are combined?
Doctors do combine them. The NIDDK page says research shows that an alpha blocker plus a 5-ARI may work better than one medicine alone. The numbers on side effects come from MTOPS, a 4 to 6 year trial of 3,047 men that appears in the Proscar label. It used finasteride and doxazosin, which is another alpha blocker, so tamsulosin is not in this table, but the pattern is the useful part.
| Side effect | Placebo | Doxazosin | Finasteride | Both |
|---|---|---|---|---|
| Abnormal ejaculation | 2.3% | 4.5% | 7.2% | 14.1% |
| Impotence | 12.2% | 14.4% | 18.5% | 22.6% |
| Decreased libido | 5.7% | 7.0% | 10.0% | 11.6% |
Two things stand out. First, the effects add up: abnormal ejaculation in the combination group (14.1%) was close to the sum of the two single drugs, which is exactly what the label says. Second, look at the placebo column. Over 4 to 6 years, 12.2% of men taking only a sugar pill reported impotence, and 5.7% reported lower libido. Men over 50 with an enlarged prostate already have a fair share of sexual changes, with or without a pill, so the medicine is rarely the whole story.
How to read these numbers
Sexual side effects are real, and they are also a minority experience. In the trials behind the labels, most men did not report them, the finasteride effects were concentrated in the first year, and the placebo groups show how common these changes already are at this age. That makes the sexual side effects a good reason for an honest conversation with your doctor, not a reason to avoid treatment that your symptoms may call for.
Erection trouble has many causes beyond medicines, and we cover the wider picture in our men's vitality guide.
What else should I know about these medicines?
The sexual effects are only part of what the labels say. These are the other points worth having in your head before the appointment:
- Dizziness and fainting (tamsulosin). MedlinePlus says tamsulosin may cause dizziness, lightheadedness and fainting, especially when you stand up quickly. In the table above, 15% of men on 0.4 mg reported dizziness against 10% on placebo. The NHS says to sit or lie down if you feel dizzy and not to drive.
- Eye surgery (tamsulosin). MedlinePlus says to tell your doctor if you need eye surgery. The FDA label explains why: a condition called intraoperative floppy iris syndrome has been seen during cataract surgery in men on or previously on alpha blockers, so tell your eye surgeon you take or took one.
- PSA (finasteride). The label says finasteride reduces PSA by about 50% within six months, so tell your doctor and the lab. Our PSA test guide explains how the number is read.
- Women and pregnancy (finasteride). MedlinePlus says women who are or may become pregnant should not touch broken or crushed finasteride tablets. Whole, coated tablets are fine to handle, according to the label.
- Prostate cancer. The label says finasteride may increase the risk of high-grade prostate cancer: in the 7-year PCPT trial, Gleason 8-10 cancers were found in 1.8% of men on finasteride and 1.1% on placebo. That is one more reason the PSA conversation with your doctor matters.
For the full picture of the prostate and what else is worth knowing, our complete prostate guide is the place to start.
What should I ask my doctor?
A short list for the appointment, so the question you were afraid to ask is on paper:
- Which of these two families fits my symptoms best, and what should I notice in the first weeks?
- What are the chances of ejaculation, erection or libido changes with this particular medicine?
- If I notice a change, what should I do, and is a different dose or medicine an option?
- Are any of my other medicines (blood pressure pills, for example) likely to add to the dizziness or the sexual effects?
- Will I need a PSA test, and how will you read it while I am on finasteride?
- I have cataract surgery coming up (or may have it): do I need to tell the eye surgeon about this medicine?
A good doctor has heard all of these before. Most men leave that visit with a plan they can live with, and with the confidence to call back if something changes.
Frequently asked questions
Do tamsulosin and finasteride cause erectile dysfunction?
Finasteride can: in the first year of the 4-year trial behind the FDA label, 8.1% of men on finasteride reported impotence against 3.7% on placebo, and in years 2 to 4 the rate was the same in both groups (5.1%). Tamsulosin is listed for ejaculation changes and dizziness rather than erection problems, although MedlinePlus lists a painful erection that lasts for hours as a rare, serious effect that needs a call to the doctor right away.
What is retrograde ejaculation, and is it dangerous?
Retrograde ejaculation means semen goes backward into the bladder instead of out through the penis. MedlinePlus says it is usually not a problem unless you are trying to conceive, and that if a medicine is the cause, stopping it often restores normal ejaculation. Cloudy urine after orgasm is one sign. Tell your doctor if it bothers you.
Do the sexual side effects of finasteride go away?
For most men they fade: the FDA label says there is no evidence of more sexual side effects with longer treatment, and new reports decreased the longer men stayed on it. The label and the NHS both add that some men have reported sexual problems that continued after stopping, and the label says the role of the medicine in those cases is unknown. If the effects bother you, your doctor is the one to talk to, and you should not stop on your own.
How long does finasteride take to work for BPH?
MedlinePlus says it may take at least 6 months before BPH symptoms improve. It works by changing the size of the gland, and that takes time. Ask your doctor what to expect from tamsulosin, since its MedlinePlus page gives no timeline.
Can I take tamsulosin and finasteride together?
Yes, doctors do prescribe them together. The NIDDK says research shows that a combination of an alpha blocker and a 5-alpha reductase inhibitor may work better than one medicine alone. The trade-off is that side effects add up: in the MTOPS trial, abnormal ejaculation was reported by 14.1% of men on finasteride plus doxazosin, against 7.2% on finasteride alone and 4.5% on doxazosin alone.
Does finasteride change my PSA test?
Yes. The FDA label says finasteride reduces PSA by about 50% within six months, so a new baseline should be set at least six months after starting. Tell your doctor and the lab you take it. Our article on the PSA test after 50 covers how doctors adjust for that.
Should I stop my BPH medicine if the side effects bother me?
Do not stop on your own. MedlinePlus says tamsulosin controls BPH symptoms but does not cure the condition, and advises talking to your doctor before stopping. A change in dose, timing or medicine is something to decide together with your doctor, and sexual side effects are a normal thing to bring up.
Sources we checked for this article
- MedlinePlus (National Library of Medicine): Tamsulosin (last revised December 2025)
- MedlinePlus (National Library of Medicine): Finasteride (last revised June 2026)
- FDA: Proscar (finasteride) prescribing information (revised March 2026)
- DailyMed (National Library of Medicine): Flomax (tamsulosin) capsules, FDA-approved label
- NIDDK: Enlarged Prostate (Benign Prostatic Hyperplasia) (last reviewed June 2024)
- NHS: Side effects of finasteride (page last reviewed August 2023)
- NHS: Side effects of tamsulosin (page last reviewed February 2023)
- MedlinePlus Medical Encyclopedia: Retrograde ejaculation (reviewed January 2025)