Antidepressants and Tamoxifen

Hi I’ve just been diagnosed with breast cancer it has been caught very early and although they are going to do a masectomy they do not think I will need radio or chemo therapy which is great. They have put me on Tamoxifen but I also take paroxatine which I have done for a number of years. My consultant does not seem worried about the two but did say my GP might have a problem with it. I suffer from anxiety and I can’t possibly stop my paroxatine especially now my anxiety and panic attacks have been awful since being diagnosed. Any advice welcome.

Hi Cola,
First of all, welcome.
It’s good to hear your bc was picked up early & although you need it like a hole in the head, from what you say, it looks like it will be straightforward to treat from the bc point of view.
Others here do have antidepressant treatment with tamoxifen & hopefully will be along to advise. It also might be an idea to post in ‘hormone therapy’ &/or the ‘ask our nurses’ section of the forum. Also, do have a chat with your GP about it.
ann x

Hi, I’m a doctor. Paroxetine and fluoxetine should not be used with tamoxifen as they make the tamoxifen less effective. There are other alternatives to paroxetine in the same family which do not interact anything like as much, such as sertraline and citalopram. Suggest you talk to your GP about it.

I’m on sertraline and will be on tamoxifen after chemo. Just to warn you, if changing from paroxetine, it can take a long time to come off as you may need to reduce very slowly as side-effects from reduction can be nasty (paroxetine is particulaly bad for this I’m afraid)

Also the anxiety will improve a bit once treatment is underway, the bit at the beginning when you’re waiting all the time makes everyone anxious, but it does get better.

I’m not a doctor but I strongly believe my early breast cancer was caused by Paroxetine and if you Google studies you will find a link. You can taper off slowly and replace it with a safer antidepressant. 

I have found a link to a study which would suggest paroxetine may actually have the opposite effect i.e. helping kill breast cancer cells. So I wouldn’t necessarily give up on the paroxetine.

Paroxetine Induces Apoptosis of Human Breast Cancer MCF-7 Cells through Ca2±and p38 MAP Kinase-Dependent ROS Generation

Apologies for size and boldness of the title above…


There is only a link if you take it with tamoxifen. That’s probably what you meant but I thought it good to clarify in case someone reads and thinks that paxil caused their first breast cancer.

Thank you for adding that Kay


It is a galactagogue and can cause milk production after breastfeeding or in people who have never breastfed, therefore I don’t trust it. I breastfed for 18 months, stopped for a year, started taking paroxetine, started producing milk again and a year later found a lump age 29. No family history of breast cancer. 

From the study you posted, “Antidepressants have shown anticancer potential in a variety of cancer cells, but the use of antidepressants for the treatment of cancer is controversial among researchers. Some studies show that use of antidepressants increases breast cancer risk, but some studies do not agree with this view” - it’s a personal choice, but I’m not risking it. 

Thank you for your contribution Mermaid. 


Hi Mermaid. That’s a really old study you posted. In breast cancer world, research and results happen so quickly that I wouldn’t be apt to trust a study with data use from the 90’s. Here’s a much newer more comprehensive study stating there is no link -

Hi, I’m aware it’s an older article so I did a Google Scholar search and custom filtered from 2019 using just “SSRIs breast cancer” as the search term.

and from 2018: 


This was a significantly large cohort study and concluded, 

“In this large breast cancer cohort, SSRI use was associated with a 27% increase in breast cancer mortality. The cause of this is unknown; however, confounding by indication seems likely as it was largely attenuated when restricting to patients with prior depression, or when comparing SSRIs to other antidepressant medications. Clinicians should not be unduly concerned when prescribing SSRIs to breast cancer patients, but the increase in mortality among long-term SSRI users warrants further investigation.”

As someone who is trying to find the least-risk antidepressant post-Tamoxifen, I’m concerned by the 27% increase in breast cancer mortality cited in the large cohort study. The cause might be unknown, but I’m more concerned with staying alive than finding out the cause.

I was told repeatedly by clinicians, including a specialist consultant, that I couldn’t have breast cancer in my late 20s/early 30s and accepted their medical expertise despite symptoms to the contrary. I did have breast cancer, in the exact location that I first went to the first GP with a lump at age 29. If I’d been referred then, I may not have needed such aggressive treatment seven years later.

I’ve also been told by two GPs in recent years that it’s fine to take HRT after 14 years NED, when NICE guidelines and my oncologist clearly say no. 

4.5 years into menopause, I’d love to be able to take HRT and any effective antidepressant medication but I’m risk-averse. Apologies if this worries anyone. 

Oh I’m risk adverse, too. Completely get it Mermaid. I don’t know if this will give you any comfort but I go to a top rated NCI hospital in the US and asked them about SSRI’s. Their response word for word is below.

"There is no strong trial data to show that SSRIs increase breast cancer mortality. These studies that report a link are not base in randomized controlled trial data. There is a large meta-analysis that actually shows a decrease in GYN cancers and shows no link in breast cancer recurrence or mortality.

No need to stop or taper off for this reason."

However, in doing research effexor seems to have the least interaction with tamoxifen and also, like the other other SSRI’s, shows an ability to help with menopausal side effects such as hot flashes. In fact, I am thinking I may try to switch to that with a psychiatrist’s help and support since it also helps with ADHD (which I have). In regards to your GP I am so sorry they have given you quite bad advice and info. They aren’t cancer experts though and considering the nature of their job I doubt many keep up with research in regards to it. I like my GP but I don’t ever plan to take any of her advice in regards to breast cancer unless I run it by my oncologist first. In the US I will have access to my oncologist probably for a decade or more.  

Yes, I was in Effexor during Tamoxifen and tapered off it afterwards - it seems less risky. I was discharged from oncology years ago on the NHS so have to do my own research.