Updated by the Progyny Editorial Team. Reviewed by Philip Cheng, MD — October 2025.
Testosterone deficiency (also known as low testosterone, “low T,” or hypogonadism) is common, affecting 4 to 5 million people in the United States. Testosterone levels often start to decline around age 30. About 7% of people with testicles in their 50s have low testosterone, and that number goes up with age.
What is testosterone?
Testosterone is a hormone naturally produced by everyone, but it has stronger effects for people assigned male at birth (testosterone is produced mainly in the testicles). Testosterone is critical for sexual development, sperm production and fertility, sex drive and sexual function, and building bone and muscle mass.
Signs of testosterone deficiency
Testosterone is known as a sex hormone, but it is essential for the functioning and development of the male body.
Signs of testosterone deficiency include:
- Low sex drive
- Erectile dysfunction
- Reduced semen volume and lower sperm count
- Fatigue and sleep issues
- Difficulty with exercising and gaining muscle
- Weight gain
- Increased body fat
- Decreased bone density
- Mood swings
- Low motivation
- Impaired concentration/memory
- Smaller than usual penis or testicles
- Anemia
How does testosterone deficiency affect fertility?
Testosterone deficiency can lead to lower sperm counts, affecting fertility.
But this is important: taking testosterone harms fertility.
That might be the exact opposite of what you’d expect. But when you take testosterone produced outside the body, the body will sense that testosterone levels have gone up. In response, the testicles will lower or stop sperm production.
If you want to maintain your fertility and treat symptoms of low testosterone, work with your healthcare provider. There are some medicines that will not lower sperm production and may even help boost sperm counts.
What causes testosterone deficiency?
Testosterone naturally declines with age. In addition, some conditions can cause testosterone deficiency in people of all ages, including children.
Some conditions affect the testicles directly, leading to low levels of testosterone (primary hypogonadism). This can include inherited conditions, certain illnesses, injuries, and some cancer treatments.
With secondary hypogonadism, testosterone deficiency is due to damage to the pituitary gland or hypothalamus, which control hormone production in the testicles. This damage may be from inherited conditions, or happen from aging, being overweight, or medicines including opioids and anabolic steroids.
How is it diagnosed?
Typically, a diagnosis of testosterone deficiency depends on two things:
- Having signs of testosterone deficiency
- Low testosterone levels (below 300 ng/dL) in a blood test
Two separate blood tests are needed for confirmation. They should be done in the early morning on non-consecutive days. This is because testosterone levels are at their peak in the morning and change throughout the day.
What are the treatment options?
In general, things that are good for your health (such as eating healthy foods and staying at a healthy weight) can help boost testosterone levels.
Certain foods that are rich in vitamin D and zinc can help boost testosterone. Some examples include fish, low-fat milk enriched with vitamin D, egg yolks, oysters and shellfish, and legumes.
However, diet alone is often not a cure for testosterone deficiency.
Medicine is often necessary, and it can come in many different forms, including injections, pills, skin gels/patches, pellets implanted under the skin, and nasal gels. Almost all of these will lower sperm production (lower fertility).
Who diagnoses and treats testosterone deficiency?
Many primary care physicians don’t have specialized training for testosterone deficiency. They may not be familiar with all of the hormone medicines available, especially the fertility-friendly options.
Your best option is to see a reproductive urologist who specializes in testosterone deficiency and male infertility. They’ll work with you to understand your history and goals to find the right treatment path for you.
Your Progyny Care Advocate is also here to help provide more information and answer questions you may have along the way.
Disclaimer: The information provided by Progyny is for educational purposes only and is not medical advice. Always consult a qualified healthcare provider for medical guidance.