What is TRT? Complete Guide to Testosterone Replacement Therapy

What is Testosterone?

Testosterone is the primary male sex hormone, responsible for developing male characteristics during puberty and maintaining them throughout adulthood. It plays a critical role in:

• Muscle mass and bone density
• Sex drive (libido) and erectile function
• Energy levels and mood regulation
• Red blood cell production
• Fat distribution and metabolism
• Cognitive function and mental clarity

Testosterone levels naturally peak in the late teens to early 20s and begin declining around age 30, typically by 1-2% per year. When levels drop below the clinical threshold — generally 300 nanograms per deciliter (ng/dL) — and symptoms are present, a physician may diagnose hypogonadism and recommend TRT.

Who Needs TRT?

TRT is prescribed for men with clinically diagnosed hypogonadism, which means both:

1. Blood test confirmation showing testosterone levels below 300 ng/dL (measured via morning blood draw when levels are highest)
2. Symptoms of low testosterone including chronic fatigue, decreased libido, mood disturbances, muscle loss, weight gain, or cognitive decline

According to the American Urological Association, an estimated 2-6% of menhave clinically low testosterone. However, some researchers believe the actual number may be higher, as many men don't get tested or attribute symptoms to aging.

Common causes of low testosterone beyond aging include obesity, type 2 diabetes, chronic stress, sleep disorders, certain medications (especially opioids), pituitary conditions, and testicular injury.

Types of TRT

There are several methods of administering testosterone, each with its own advantages and considerations:

1. Injectable Testosterone

The most common and cost-effective form. Testosterone cypionate or enanthate is injected intramuscularly (typically into the thigh or glute) every 1-2 weeks, or subcutaneously 2-3 times per week for more stable levels.

• Pros: Most affordable, well-studied, flexible dosing
• Cons: Requires self-injection, possible fluctuations between doses

2. Topical Gels

Applied daily to the shoulders, upper arms, or abdomen. Brand names include AndroGel and Testim.

• Pros: Easy to apply, steady hormone levels
• Cons: Risk of transferring to others through skin contact, more expensive

3. Transdermal Patches

Applied daily to the skin, typically on the back, abdomen, or upper arm. Provides a steady release of testosterone.

• Pros: Consistent delivery, no injection needed
• Cons: Skin irritation common, less flexible dosing

4. Subcutaneous Pellets

Small pellets implanted under the skin (typically in the hip area) every 3-6 months. Provides the most consistent testosterone levels.

• Pros: Longest-lasting, most stable levels
• Cons: Requires minor surgical procedure, can be expelled

5. Oral/Nasal Options

Newer options like Jatenzo (oral) and Natesto (nasal gel) offer non-injection alternatives, though they're typically more expensive and may have limitations.

Benefits of TRT

When prescribed appropriately and monitored by a physician, TRT can provide significant improvements:

• Increased energy — Many men report noticeable improvement in energy levels within 3-6 weeks
• Improved libido — Sexual desire and function typically improve within 3-6 weeks
• Better mood — Reduced depression and irritability, improved sense of well-being
• Muscle and strength gains — Increased lean muscle mass and strength with consistent training (3-6 months)
• Fat loss — Improved body composition and metabolism
• Cognitive improvement — Better focus, memory, and mental clarity
• Bone density — Reduced risk of osteoporosis over time

Risks and Side Effects

Like any medical treatment, TRT carries potential risks that require monitoring:

• Polycythemia — Increased red blood cell count, requiring regular blood monitoring
• Acne — Oily skin and breakouts, especially in the first few months
• Sleep apnea — May worsen existing sleep apnea
• Fertility impact — Can reduce sperm production (usually reversible)
• Testicular atrophy — Testes may shrink due to reduced natural production
• Cardiovascular — Some studies suggest potential cardiovascular risks, though evidence is mixed

Regular blood work (typically every 3-6 months) is essential to monitor these potential side effects and adjust dosing as needed.

Read our complete guide to TRT side effects →

How to Get Started with TRT

The process for starting TRT through an online clinic is straightforward:

1. Get blood work done — Most online clinics provide an at-home blood test kit that you complete and mail back
2. Consult with a physician — Review your results with a licensed doctor via video call
3. Receive your prescription — If clinically appropriate, your medication is shipped to your door
4. Begin treatment and monitor — Start therapy with ongoing physician oversight and regular lab work

Online TRT clinics like PeterMD have simplified this process, making it possible to start treatment from the comfort of your home, with plans starting at $99/month (lab testing is billed separately).