For all its reputation, testosterone plays a much bigger role in the body than one might think.

A type of sex hormone, testosterone indeed helps regulate libido and sexual function in men (and women, it should be added). But it's also responsible for maintaining muscle mass, bone density and fat distribution, and it can even affect your mental wellbeing.

Lots of things can affect testosterone levels, including lifestyle factors like diet, sleep, stress and weight. Age can too, as the glands responsible for regulating testosterone decline over time, along with certain medical conditions like diabetes and genetic disorders.

Whatever the cause, low levels of testosterone can not only result in a decline in sex drive and function, but can also contribute to a range of symptoms, including decreased muscle mass, weight gain, mood changes, fatigue and even osteoporosis (weakening of bone).

All told, nearly 40 percent of men over 45 and over half of men over 75 experience low testosterone, according to Dr. Akhil Muthigi, a urologist at Houston Methodist.

While in some cases low T can be treated with lifestyle changes, testosterone replacement therapy (TRT) can be an effective treatment option when healthy habits aren't enough. Dr. Muthigi discusses these treatment options, as well as the signs and symptoms of low T that he advises men shouldn't ignore.

What are the signs and symptoms of low testosterone in men?

Low testosterone is sometimes referred to as male hypogonadism, but they're actually two distinct diagnoses, according to Dr. Muthigi. Low testosterone is a specific diagnosis in which a man's total testosterone measures below 300 nanograms per deciliter (ng/dL), whereas a hypogonadism diagnosis consists of both a low testosterone result and specific clinical symptoms. Those may include:

• Low libido
  
• Low energy and depression
  
• Other changes in mood or cognition
  
• Anemia
  
• Fatigue
  
• Erectile dysfunction
  
• Male factor infertility
  
• Increased body fat
  
• Decreased muscle mass
  
• Breast tissue formation

In other words, it's possible that some men may experience low testosterone despite not having any of the hallmark symptoms associated with hypogonadism. Without a testosterone test, they wouldn't even know it was low.

What causes men to develop low testosterone or hypogonadism?

Until they reach their 30s, most men have fairly constant levels of testosterone, which is controlled by a complex system involving the testicles, the hypothalamus and pituitary gland in your brain.

As men age, their hypothalamus and pituitary gland function gradually decline, leading to lower production of testosterone from the testes, according to Dr. Muthigi. In fact, there is always an age-related decline with testosterone, he says, but the rate differs in every man, depending on their genetics and lifestyle.

Age, however, is but one of many possible causes of low testosterone and hypogonadism. In fact, there are many reasons why a man might experience symptoms associated with hypogonadism. Those most common, according to Dr. Muthigi, include:

• Certain infections, especially mumps
  
• Radiation therapy
  
• Injury or trauma to the testes, pituitary gland or adrenal glands
  
• Obesity and metabolic syndrome
  
• Certain medications such as chemotherapy drugs, steroids and opioids
  
• Excessive alcohol intake or smoking
  
• Certain chronic diseases such as diabetes, kidney failure or liver cirrhosis
  
• Certain genetic predispositions and mutations
  

How is low testosterone initially treated?

Depending on the cause and diagnosis, Dr. Muthigi treats low testosterone in a couple different ways, including lifestyle changes and medical supplementation.

"First, I first promote healthy lifestyle habits, all of which can naturally boost testosterone production," he says. "That includes regular exercise, both strength training and cardio; adequate sleep; stress management; a nutrient-rich diet high in protein; and weight loss if applicable."

In the event these practices fail to raise a patient's testosterone levels naturally, Dr. Muthigi says he then introduces the idea of external testosterone supplementation, or testosterone replacement therapy (TRT).

"In my practice and most other andrology-focused practices, if a patient meets the criteria of hypogonadism, I offer testosterone therapy as long as there are no contraindications that make it unsafe for them to take," Dr. Muthigi says. "Such conditions or factors may include a desire to maintain their current or future fertility, a recent heart attack or stroke, certain advanced prostate cancers that require hormone therapy, among others."

How does testosterone replacement therapy work?

"The andrology field has progressed tremendously just within the last decade, as there are newer FDA-approved testosterone formulations that are safe and efficient," says Dr. Muthigi. "There are several different forms of testosterone supplementation, including topical gels, nasal sprays, oral tablets and short- and long-acting injections, all of which have their pros and cons."

Testosterone gels and other external patches offer non-invasive ways to boost your testosterone, as the medication is absorbed through the skin barrier and into your bloodstream. However, it's important that the gel not come into contact with anyone else, as they might accidentally absorb it themselves.

Testosterone nasal spray also contains a type of gel but doesn't carry the risk of transference. Instead, the medication is applied into the nose and absorbed there through the nasal lining. However, it requires more frequent application than any of the other medications.

Injections of testosterone are also common and may be ideal for those who don't eat breakfast, have absorption issues or have personal concerns surrounding gels and transference.

Finally, there is oral testosterone, which over the decades underwent a rise, then fall in popularity, when those formulations were found to increase the risk of liver toxicity. Today, however, the newer oral formulations do not carry any of the associated livery toxicity concerns and is more readily absorbed, says Dr. Muthigi.

"The form of testosterone we ultimately decide upon involves shared decision-making with the patient based on their goals and preferences," says Dr. Muthigi.

What are the potential side effects of testosterone replacement therapy?

In 2015, the FDA announced that it would require drugmakers to issue a new warning label surrounding testosterone and cardiovascular safety. The agency cited certain studies that found testosterone therapy increased the risk of heart attack and stroke.

However, in February 2025, after reviewing a "large clinical trial," the FDA announced several label changes to testosterone drugs. Chief among them was the removal of the black box warning from all testosterone products that stated the drugs could lead to increased risk of cardiac events. Ultimately, the clinical trial published in the New England Journal of Medicine and cited by the FDA concluded that testosterone therapy did not increase cardiovascular risk.

"A growing body of recent evidence shows testosterone to be safe from cardiovascular standpoint," says Dr. Muthigi. "In fact, low testosterone and hypogonadism is associated with higher cardiovascular risk."

Erectile dysfunction is one such symptom of low testosterone that may also be an indicator of poor blood circulation caused by atherosclerosis, or narrowing of the arteries.

(Related: How Low T Affects Heart Disease Risk)

"There is also a growing body of evidence that demonstrates testosterone is safe to administer in men with prostate cancer or previously treated prostate cancer," Dr. Muthigi adds. "However, this must be managed and monitored by an andrology specialist."

Ultimately, like most medications, testosterone therapy is not without risk. The known risks include a decrease in fertility and sperm count; elevated blood counts (polycythemia), which can lead to blood clots if not monitored properly; acne; breast enlargement; and hot flashes.

Your personal risk, however, including the contraindications cited above, can vary and should be discussed further with an andrology specialist.

When to seek treatment for low testosterone

"If men harbor any of the hallmark symptoms of low T and hypogonadism, I advise they meet with an andrology specialist for a thorough history and physical exam and to have their testosterone levels checked," says Dr. Muthigi.

This will include a blood test taken in the morning between 7 and 9 a.m., during which your testosterone levels are typically the highest, along with a complete hormone lab workup if needed, he says.

(Related: 6 Signs to See a Men's Health Specialist)