Flomax side effects

Posted by lifutang @lifutang, Jun 18, 2025

During proton therapy for prostate cancer, I took Flomax to address urinary issues. However, I experienced headache, dizziness, low blood pressure, and even fainted after standing up from a sitting position. I would like to ask if any fellow patients have helpful suggestions for managing these side effects of this medication.

Interested in more discussions like this? Go to the Prostate Cancer Support Group.

Profile picture for pcrich @pcrich

I've been taking Flomax a year now. RO prescribed it and told me to take in the evenings. I still have to get up 2-3 time a night with little volume each time. During the day I can generally go a few hours before I feel the need to go. Volume is more but then I drink more liquids. The up 2-3 times (almost like clockwork - every 2 - 2.5 hrs. each time) really disturbs my sleep. Should I change the timing on taking it?

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@pcrich I take it in the morning, and still have to get up every 2 hours to evacuate my bladder. I’ve been taking it for about 14 months now with continued Orgovyx treatment. The dizziness is an ongoing issue, especially if I’m working out.

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I have been on Flomax 10 weeks, it did what it purported to do, I’m not getting up 5 times in the night, thats terrific. I still get up at least twice however. My main concern is the tiredness, I have napped more in 2 months than in the previous 50 years, I’m just not one to nap in the pm. Lower pressure although not significant seems to be the culprit. Flomax has other side effects that come and go, such arcGI upset, headache which has abated. Somewhat concerned regarding eye involvement as at my age cataracts are just around the corner.

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Profile picture for grandmira @grandmira

I have been on Flomax 10 weeks, it did what it purported to do, I’m not getting up 5 times in the night, thats terrific. I still get up at least twice however. My main concern is the tiredness, I have napped more in 2 months than in the previous 50 years, I’m just not one to nap in the pm. Lower pressure although not significant seems to be the culprit. Flomax has other side effects that come and go, such arcGI upset, headache which has abated. Somewhat concerned regarding eye involvement as at my age cataracts are just around the corner.

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@grandmira
Interesting information. Flomax is normally used for people that have flow problems not really to treat urgency.

You can use Myrbetriq or Gemtesa for urgency and incontinence issues. I’ve been on Myrbetriq For almost 2 years now and seldom get up at night to pee, Usually, I can wait till the morning. Didn’t used to be that way I would wake up and feel like I had to go more than once in the middle of the night.

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My issue was not enough flow hence frequent trips 5+ to the washroom in the night, rough on the sleeping. It works but as I said there are side effects, tiredness is the most prevalent.

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Profile picture for grandmira @grandmira

My issue was not enough flow hence frequent trips 5+ to the washroom in the night, rough on the sleeping. It works but as I said there are side effects, tiredness is the most prevalent.

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@grandmira
So what you’re getting at is you’re still having flow problems and can’t empty your bladder. As a result, you need to get up multiple times.

I was speaking to someone a couple of days ago who was on Flomax and stopped because it lowered his blood pressure, and that could cause fatigue.

Do you feel your blood pressure is being lowered by it? Have you tested it to find out if maybe that’s the reason you’re tired.

Are you on drugs for prostate cancer? ADT can cause a lot of fatigue as some of the other ARPI drugs like Xtandi. If you’re not on any of these drugs, you might want to take this over to The forum that discusses urinary issues. If you are on these drugs, then the fatigue may be as much due to the drugs as Flomax.

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Profile picture for Jeff Marchi @jeffmarc

@grandmira
So what you’re getting at is you’re still having flow problems and can’t empty your bladder. As a result, you need to get up multiple times.

I was speaking to someone a couple of days ago who was on Flomax and stopped because it lowered his blood pressure, and that could cause fatigue.

Do you feel your blood pressure is being lowered by it? Have you tested it to find out if maybe that’s the reason you’re tired.

Are you on drugs for prostate cancer? ADT can cause a lot of fatigue as some of the other ARPI drugs like Xtandi. If you’re not on any of these drugs, you might want to take this over to The forum that discusses urinary issues. If you are on these drugs, then the fatigue may be as much due to the drugs as Flomax.

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@jeffmarc
No cancer issue, just BPH . Flomax relaxes the bladder neck and prostate tissue so as to relax the “strangle” hold that Prostate growth has on the urethra. It’s effective, getting up twice inside of five times a night, but with some side effects that are quite annoying i.e. tiredness from lower blood pressure, GI upset.

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Profile picture for grandmira @grandmira

@jeffmarc
No cancer issue, just BPH . Flomax relaxes the bladder neck and prostate tissue so as to relax the “strangle” hold that Prostate growth has on the urethra. It’s effective, getting up twice inside of five times a night, but with some side effects that are quite annoying i.e. tiredness from lower blood pressure, GI upset.

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@grandmira
There is a bladder Group in Mayo. You might want to post over there and get people’s ideas on what to do to make things even better.

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Profile picture for dogrocketp @dogrocketp

@pcrich I take it in the morning, and still have to get up every 2 hours to evacuate my bladder. I’ve been taking it for about 14 months now with continued Orgovyx treatment. The dizziness is an ongoing issue, especially if I’m working out.

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@dogrocketp
I tried Flomax for hesitancy, instead of 4 to 5 trips to the bathroom each night went to 3 to 4. Also lots of light headedness. I tried alfuzosin, it didn't work as well as Flomax and the side effects were worse. I am now taking 4mg of silodosin with the evening meal with an acetaminophen and an ibuprofen at bed time. I get up to pee once or twice a night, occasionally I don't get up at all

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Profile picture for dogrocketp @dogrocketp

@pcrich I take it in the morning, and still have to get up every 2 hours to evacuate my bladder. I’ve been taking it for about 14 months now with continued Orgovyx treatment. The dizziness is an ongoing issue, especially if I’m working out.

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@dogrocketp
Forgot to mention side effects with silodosin. Sometimes when I bend over multiple times to pick things up, I get lightheaded.

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You may find with time that your blood pressure regulates. I was on a blood pressure medication when I went on Flomax and by BP dropped so I had to cut my BP med in half but after 3-4 months BP increased and I had to resume m original dose

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