Tamoxifen 10mg vs 20mg

Posted by jeannie53 @jeannie53, Jun 25, 2019

I was on Anastrozole for 6 months my doctor switched me to Tamoxifen because of severe muscle pain. I was given 20mg of Tamoxifen is that the regular dosage every day. It also comes in 10mg. I saw a study that women were given 5mg each day by cutting the 10mg in half and was wondering if anyone has cut their dosage so it is better tolerated.

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billiemoore | @billiemoore | Dec 25, 2025

I wasn’t willing to try 20mg because of my sensitivity to meds —said I would take European dosage, 10mg. I get some side effects but manageable and will be staying on 10mg indefinitely.

jmab | @jmab | Dec 25, 2025

In reply to @pacentro "@jmab I am 78, and I am not taking anything. If I get a recurrence, I'll..." + (show)

@pacentro I completely understand. It's definitely asking a lot for women our age to take a harsh medicine which is really only seeing as a preventive. I wish there were easier treatments.

jmab | @jmab | Dec 25, 2025

In reply to @billiemoore "I wasn’t willing to try 20mg because of my sensitivity to meds —said I would take..." + (show)

@billiemoore this is very interesting to me. I also opted for the 10 mgs Tam which I'm supposed to start next week. I didn't know it was considered a European dosage. I'm 72. Would love to hear about your side effects on 10 mg. I'm glad you're finding it tolerable. I am so hoping I can handle it! (And Happy Holidays!)

Colleen Young, Connect Director | @colleenyoung | Jan 4 4:04pm

In reply to @marygb "@colleenyoung Hi Colleen, No I am not. I’m scared of the necrosis of the jaw side..." + (show)

@marygb, lifestyle approaches for managing osteoporosis are really important. Sometimes lifestyle (diet, exercise, supplements) are not enough however. It is important to stay in communcations with your oncologist and endocrinologist when medications may be necessary to prevent spinal fractures or other serious effects of poor bone health.

Here's some info from Mayo Clinic to help inform your discussions:
- Osteoporosis treatment: Medications can help https://www.mayoclinic.org/diseases-conditions/osteoporosis/in-depth/osteoporosis-treatment/art-20046869
- Osteoporosis https://www.mayoclinic.org/diseases-conditions/osteoporosis/symptoms-causes/syc-20351968

Arvind Natarajan | @malebreastcancer47 | Jan 4 4:10pm

In reply to @marygb "Hi jamb, no I didn’t. I can’t stand the thought of the side effects. There have..." + (show)

@marygb I had stage 1 breast cancer, 4 rounds of chemo and due to my oncotype dx score of 34, I was asked to take 20 mg Tamoxifen. After 1 yr, I could not handle the side effects and my oncology team, lowered the dose to 10 mg. They also said they are doing a study on LowTam or 5 mg however was told this is for an oncotype dx score of 15 or less.
They do not know how effective it is in preventing reoccurrence if 10mg or 5 mg is prescribed.

marygb | @marygb | Jan 4 5:24pm

In reply to @malebreastcancer47 "@marygb I had stage 1 breast cancer, 4 rounds of chemo and due to my oncotype..." + (show)

@malebreastcancer47
I have a oncotype score of 22. My oncologist preferred I take an AI with bone meds. I did go on an AI for a couple months which caused very achey joints and hairloss not to mention I found out I had osteoporosis. I was not
willing to take the bone
meds so she agreed to the 5 mg tamoxifen. I read about a study being done in Italy and though it is not completed the lower dose looks pretty promising. You should be able to google it and read more about it. There’s also a new med that’s set to be released later this year which is more effective than the meds they have now. I’m going to try that one once approved. It’s a very hard decision. I hope and pray that all of us find something that will work.

ritalu | @ritalu | Jan 5 11:14am

I am taking 5 mg of tamoxifen daily. I have a friend who is taking 10 mg every other day. She does not feel any side affects. With the 5 mg, I feel fatigue and need to rest for about 20 minutes after taking the dosage. I had stage 0 DCIS - two lumpectomies - surgeries (second surgery 6 mos. after radiation) This might contribute to the fatigue.

luckbme | @luckbme | Jan 8 8:15pm

I have been blaming tamoxifen for my terrible side effects. I had IDC, lumpectomy, 15 sessions of radiation and all went very well. I felt good, actually. Then started tamoxifen and took for 10 weeks before I realized I could not live with those side effects and quit taking mid-April. Although the side effects are dwindling now, January 8, 2026, but still have some every day for a few hours, I'm wondering if the radiation caused the side effects. I started the tamoxifen immediately after the radiation, so it's hard to say. The tamoxifen, 10mg, has half life of 50 hours. Something is not adding up. Anyone?

Arvind Natarajan | @malebreastcancer47 | Jan 8 11:01pm

I had stage 1 breast cancer. After recovery from surgery, 8 weeks later, I started on chemo. 4 infusions over 12 weeks. After 12 weeks, due to how I was feeling, I did not start Tamoxifen. Mayo said ok to waiting 1 year. I recovered from chemo effects, muscle loss, stamina, I had shortness of breath. I needed my body to heal as much as possible. 1 yr later, I started on Tamoxifen at 20 mg. The side effects was harsh and after 1 yr, Mayo oncology reduced to 10 mg.
Now I am finally feeling more normal. Able to work, sleep and do activities with minimal menopause effects.

If you have side effects, ask your doctor if you can pause the Tamoxifen until you have recovered from radiation.