Letrozole: When will I start feeling/seeing side effects?

Aromatase inhibitors lower estrogen levels by stopping an enzyme in fat tissue (called aromatase) from changing other hormones into estrogen. Estrogen can fuel the growth of breast cancer cells. [Cancer. org]
My BC is HR+, HER2- and I'm postmenopausal. So I look at Letrozole as 'playing clean up' role in my treatment regimen.

@pbnew these meds decrease estrogen below detectable levels. The estrogen fed our cancers, so disrupting it starves the cancer cells. I believe that is the idea. Your doc can explain!

Thank you for your info on manufacturers. Please tell us the info source where you learned Letrozole eliminates lingering breast cancer cells. I thought it was limited to disrupting estrogen.

My wife 43 years old just finished chemo and will begin radiation this week. She is very worried about the side effects of Lupron and was curious if anyone went with a hysterectomy instead of the Lupron or has any thoughts on this? Thank you!

You may or may not experience the severe side effects listed in the insert or what you've heard from others. Everyone responds differently. It will affect your bones so be sure your diet has proper amount of calcium and vitamin D.
Keep up regular exercise and activity level. I found muscle aches and stiffness occur when I am not doing my morning exercise routine or have been sitting for long periods such as driving for an hour or so. I am 71 yr old and have arthritis in my feet and hands, which started long before BC showed up. My experience with Letrozole is 3yr 7mo. I take 2.5mg daily in the morning with breakfast so I remember to take it. I went through early menopause in my 40's with some really wicked hot flashes so perhaps that is why the occasional warm flush I get now feels like nothing. My doctor told me hot flashes are the most common complaint he hears most from his patients on AI treatment. Letrozole is a generic so be aware there are different manufacturers and I suspect from experience, pharma manufacturers use different fillers. All contain the main ingredient as it's the purpose for our taking Letrozole or any prescribed drug. The manufacturer I like best is Teva, second is Breckenridge. My very first 90 day prescription of Letrozole was from Teva. I was doing great for months and then the pharmacy switched my prescription to Accord. Within three weeks, I noticed sharp muscle pain across my shoulders and my bladder control was off. I suspected Accord used some filler that caused this reaction - perhaps I was allergic to that ingredient. Doctor thought it was just how I was reacting to Letrozole. My suspicion was confirmed when I read postings from women in another website's forum explain how they experienced side effects with certain manufacturers. So I started contacting pharmacies within a 20 mile radius (I live in rural area) to find out where they sourced Letrozole. Most use Accord and will not even look into other options. But I finally found a pharmacist at a Walgreens who listened to me and searched for options. She was able to get Letrozole from Breckenridge as Teva version was not available. The weird pains and bladder issues disappeared within a week. So I was on Letrozole by Breckenridge for a few years. Until I received notice that the Walgreens store in our area was closing. So I scrambled again calling pharmacies and the pharmacist at local Walmart said she could order Letrozole from Teva. I had to wait several weeks for the order to come in. After taking the Teva version of Letrozole for the past few months, I am now feeling less achy than I have in years. I hope I can continue with this 'brand' until I am finished at 5 yr mark. So that's my story ... I was lucky that I didn't need chemo after my lumpectomy - only did RT and then onto AI. I didn't mess around with dosage as from what I read, Letrozole is very effective medication for eliminating any lingering breast cancer cells in my body. And that's what I want it to do even if I have to deal with some side effects. Stay positive and good luck!

My doc approved alternating days for letrozole, though I never did. The only reason they don't like splitting pills is it is not precise so dosage varies slightly.

The package insert for letrozole/Femara states that studies showed 20% of the full dose reduce estradiol below detectable levels.

I will stop my 5 years of letrozole in 8 days. When I first started I was so afraid of side effects I cut pill in half (did not have permission and did not tell the doc until later).

I started 1 whole pill after 3-4 months of spliting pill and then confessed to the doctor. Splitting is NOT recommended per package insert and they “have no data to approve efficacy of a split pill,” but that is water under the bridge now.

I’m surprised that your doc approved the split but I have always wondered if it still works.

I know Letrozole is absorbed in the jejunem where the pH is 4-6, and not in the stomach where the pH is 1-2. Even though the letrozole would have been exposed to an acidic aqueous environment, it is a stable in acid. It is soluble in dicholomethane.

Either way I’ve done 4.9 months of full dose and I’m going to celebrate when I’m done.

I hope you can tolerate the full dose.

@deluga I would think side effects from hormone suppression would take awhile. That was my experience.

However, there is another category of reaction that happen more quickly- reaction to the ingredients of the pill, especially fillers. This happened to me: neurological effects within minutes. It is a "sensitivity," "intolerance," or even "allergy" but not a side effect.

This actually happens to me with quite a few meds. If I switch manufacturers, often a medication will work fine without. (For me polyethylene glycol is one culprit).

I got TN, a type of neuropathy (nerve in the ear) on the 3rd day and it was so painful, I stopped. My oncologist said you don't get side effects that quickly so it wasn't Letrozole. I don't believe her and will not retake it or any AI since all can bring on neuropathy in older woman. I'm 81.

@deluga an immediate reaction is not likely to be a side effect from estrogen suppression but instead a reaction to inactive ingredients.

I tried anastrozole generic, then letrozole generic, then a different manufacturer, and finally brand name Femara. In my last year I did find a generic letrozole that I could take.

I really hope you share this with the integrative health folks who should realize that an immediate reaction is unlikely to be related to the active ingredient in AI's.