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Factor V Leiden and Testosterone

Testosterone is the main sex hormone found in men. It is responsible for many of the physical characteristics specific to adult males. Women have testosterone too but in much smaller amounts than in men.

Testosterone is produced primarily in the testicles and helps maintain men’s:

  • Bone density
  • Fat distribution
  • Muscle strength and mass
  • Facial and body hair
  • Red blood cell production
  • Sex drive
  • Sperm production

Men need normal amounts of this hormone to make sperm and be able to have children. This hormone also signals the body to make new blood cells, ensures that muscles and bones stay strong during and after puberty and enhances libido both in men and women. Testosterone is linked to many of the changes seen in boys during puberty.


In women, testosterone is produced by the ovaries and adrenal glands. The majority of testosterone produced in the ovary is converted to the principle female sex hormone oestradiol.

What happens to testosterone levels with age?

Testosterone levels generally peak during adolescence and early adulthood. As you age, your testosterone level gradually declines — typically about 1% a year after age 30 or 40. For older men, it’s important to determine if a low testosterone level is due to normal aging or if it is due to a disease called hypogonadism.

What is low testosterone (male hypogonadism)?

Low testosterone or male hypogonadism is a condition in which the testes (testicles, the male reproductive glands) do not produce normal amounts of testosterone. It occurs due to a problem with the testicles or with the pituitary gland that controls the testicles.

Testosterone replacement therapy, in the form of injections, pellets, patches or gels, can improve the signs and symptoms of low testosterone in these men.


The use of testosterone replacement therapy to treat hypogonadism became quite popular in the early part of the 21st century during the “low-T” fad. Testosterone prescriptions soared increasing more than 300% between 2001 and 2013. However, the fad faded in 2014, after the U.S. Food and Drug Administration warned that testosterone therapy increases a man’s risk of heart attack and stroke. Evidence suggests it’s still being prescribed to many and to some who don’t suffer from hypogonadism.

Can testosterone therapy promote youth and vitality?

As you age, testosterone therapy might sound promising. But there are a lot of misconceptions about what the treatment can and can’t do for you.

Testosterone therapy might seem like the ultimate anti-aging formula. Yet the health benefits of testosterone therapy for age-related decline in testosterone aren’t clear. Testosterone therapy can help reverse the effects of hypogonadism, but it’s unclear whether testosterone therapy would benefit older men who are otherwise healthy. Some men believe they feel younger and more vigorous if they take testosterone medications, but there’s little evidence to support that this is due to the use of testosterone. Guidelines from the American College of Physicians indicate that testosterone therapy might improve sexual function somewhat in some men, but there’s little evidence that it improves other functions, such as vitality and energy.

What are the risks of testosterone therapy for normal aging?

Testosterone therapy has various risks, including:

  • Worsening sleep apnea — a potentially serious sleep disorder in which breathing repeatedly stops and starts.
  • Causing acne or other skin reactions.
  • Stimulating noncancerous growth of the prostate (benign prostatic hyperplasia) and growth of existing prostate cancer.
  • Enlarging breasts.
  • Limiting sperm production or causing testicles to shrink.
  • Stimulating too much red blood cell production, which contributes to the increased risk of forming a blood clot. A clot could break loose, travel through your bloodstream and lodge in your lungs, blocking blood flow (pulmonary embolism).

Also, some research shows that testosterone therapy can increase your risk of heart disease. More research is needed.

Does testosterone therapy increase my risks for blood clots if I have Factor V Leiden?

There are some studies that do show that testosterone therapy increases the risks of blood clots in all populations due to the increase in red blood cell production.


There are some studies that have suggested that this risk is further increased in individuals with thrombophilia such as Factor V Leiden.

Other studies have concluded that there is no increase in risks between Factor V Leiden and testosterone therapy other than the normal increase in blood clot risks seen in the general population that carry the Factor V Leiden mutation.


As far as we know at this time, there does not seem to be enough evidence to draw a conclusion either way. The association feels more research is needed to determine if there is an increase in the risk for blood clots for Factor V Leiden carriers who take testosterone therapy.


Therefore, we recommend that you consult with your healthcare professional to discuss any additional research they may be aware of on the topic and together decide if Factor V Leiden testing would be beneficial given your situation.

Should I be tested for Factor V Leiden before starting testosterone therapy?

The current recommended testing guidelines relating to Factor V Leiden are as follows:

  • those who have venous thrombosis under the age of 50
  • those who have recurrent venous thrombosis
  • those who have a family history of venous thrombosis
  • female smokers who have suffered myocardial infarction under the age of 50
  • venous thrombosis in pregnant women or those taking oral contraceptives
  • some guidelines include women with recurrent pregnancy loss, unexplained severe preeclampsia, placental abruption as well as intrauterine fetal growth restriction

There are a few situations that are not addressed in the above guidelines that could increase your risk. The guidelines assume that you are in contact with all direct family members and are aware of any history of venous blood clots they have experienced. Also, the guidelines do not take into account other major risk factors for blood clots such as hospitalization, surgery, trauma, obesity, smoking, and immobility.


Although we feel no definite conclusions can be made at this time between an increase in blood clot risks for Factor V Leiden carriers who use testosterone therapy, we do suggest you:

  • review the guidelines above to see if any other life circumstances may warrant you being tested.
  • speak with your healthcare professional about Factor V Leiden and any additional research they may be aware of on testosterone therapy and together decide if Factor V Leiden testing would be beneficial given your situation.

The test to see if you have Factor V Leiden is not intrusive and one that your healthcare professional can perform with a simple blood test.


Ultimately, for those who do not fall within the current testing guidelines and testing is not recommended, deciding whether to be tested for Factor V Leiden is a personal decision.

The American Factor V Leiden Association is working hard to promote public awareness, provide education and be a resource for knowledge.

Our current program initiative on testing is aimed at improving testing guidelines by taking a common sense approach and looking at all variables related to the disorder.

We hope to publish an in-depth position statement on Factor V Leiden testing in the coming months.

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