Ask Dr. Marc: Is Letrazole Safe?

Dear Dr. Marc,
I’ve been experiencing secondary infertility for 16 months now trying for a 3rd baby. It’s been determined as unexplained. I ovulate, no blockages, husband is fine, etc. we tried one round of Clomid and IUI last month which was unsuccessful and I can’t take anymore Clomid because it caused my vision to be blurry. My reproductive endocrinologist has recommended letrozole as a next step.
But I am nervous because I don’t know anyone who has taken it, am leery of fertility drugs in the 1st place, and read online that the chance for multiples is lower but can be linked to birth defects. What are your thoughts?
Thank you.
Hi can’t take clomid,
It is quite common for people to be leery of fertility medication. Such fears are exacerbated if the medication has ever had a “black box” warning placed upon it, such as letrazole.  With that being said, there is ample evidence that letrazole is very safe and quite effective.  I would encourage you to consider it.
Let me give you some background on Letrazole.  Letrazole belongs to a class of drugs called aromatase inhibitors.  Aromatase is the enzyme which converts testosterone to estrogen.  Aromatase inhibitors block that conversion effectively blocking production of estrogen.  They are often used in situations where exposure to estrogen is undesired, breast cancer for example.  In the world of fertility, these drugs make the brain think that the ovaries are not producing estrogen.  Consequently, the brain sends a stronger signal to the ovaries to get them to make estrogen by making one egg (in women who do not normally ovulate), or multiple eggs (in women who ovulate normally).
The controversy with letrazole came from a small study presented in 2005 which showed a slightly higher rate of birth defects in 150 women who took letrazole as compared to the general population.  Despite that fact that since that time, many other larger studies have been conducted which did NOT find a higher rate of birth defects, the manufacturer of the medication placed a specific warning on the medication against the use for fertility.
Most current fertility specialists see this warning as politically motivated and not based on science.  This is unfortunate because it is an excellent medication which may be better than other alternatives such as clomid.
In short, I understand your fears, but there is reason to believe that letrazole is safe, effective and a reasonable alternative to clomid.  If my wife and I were going through fertility treatment, I would not hesitate to use it.
Good luck,
Dr. Marc