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Pet Rats/Tamoxifen question


QUESTION: Dear Debbie,
I've reading your booklet and your pages about the Tamoxifen but I have some doubt...
I'm sorry for my bad English, but I hope that this message is understandable.

1) In your booklet you write that it's possibile to use tamoxifen in rats, starting at the age of 18 month, to prevent tumors.
However in the experiences reported online that I've found, tamoxifen was used when the tumor was already devoloped.
So... What's the best choice? Can I use tamoxifen on my female rats or should I wait until the possible develop of a tumor?

2) I don't understand if tamoxifen is useful only againt malignant tumors or if it's useful also against benign ones and why.

3) What risks I run exactly if I give it to my pet rats?

I stop for now! :)
Thank you for your time and for your useful site and books!


Your English is very understandable!  Tamoxifen will protect against both benign and malignant tumors, but only seems to be effective for malignant tumors after they have already appeared. So, giving it as a preventative is most beneficial. However, it is probably more practical and effective to have your female rats spayed.

---------- FOLLOW-UP ----------

QUESTION: Thank you for your quick and complete answer! :)
I prefer to avoid surgery, unless absolutely necessary. So I guess I'll try to give tamoxifen to my rats... Can I put it in their water bottle?


I would not recommend putting it in their water bottle. I recommend mixing a tablet in a yummy liquid and giving it to them straight from the syringe, or mixing it in food for each one individually.

Here is some info from my Rat Health Care booklet:

Tamoxifen is readily available from human pharmacies in the U.S. and veterinarians can call in a prescription.  The dose is 3 mg/lb once a day for treatment of mammary cancer, and 1.5 mg/lb once a day for prevention.  For instance, you can mix a 5 mg tablet in 1 ml of flavoring, and the dose would be 0.33 ml/lb once a day.

Ideally it should be given for the rest of the ratís life.  However, while most rats donít object to the taste of tamoxifen at first, I know several cases where rats given tamoxifen have developed a strong reluctance to take the oral medication after a few weeks.  This can make it difficult to carry out long-term treatment.  I successfully treated one of my rats for almost a year, one month on and one month off.  Even short-term treatment can help retard the growth of cancerous mammary tumors.

In a few cases, owners have reported side effects from tamoxifen.  The most common visible side effect seems to be hair loss.  In some rats is has also seemed to cause fatigue.
A less obvious side effect of tamoxifen is that it reduces the number of platelets in the blood.  This interferes with the bloodís ability to clot.  If a rat on tamoxifen needs surgery, you should stop tamoxifen treatment for 1-2 weeks before the surgery to prevent excessive and perhaps fatal bleeding.

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Debbie Ducommun


I can answer any questions about pet rats, but you will probably be able find answers to simple questions more quickly on my website at If you have a life-threatening emergency you can try calling me at 530-899-0605. I am not usually on the computer on the weekend.


I have been "The Rat Lady" since 1985 and am recognized as one of the world's experts on pet rats. I have 3 published books and already answer lots of questions about rats daily.

President of Rat Assistance & Teaching Society

I am a monthly columnist for Pet Business magazine, and my writing has appeared in other magazines. I have 3 published books.

BA in Animal Behavior

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