Penis growth is driven by hormones, primarily testosterone and a more potent form called dihydrotestosterone (DHT). These hormones act on genetically determined receptors to trigger growth in two key windows: before birth and during puberty. By the late teens, growth is essentially complete, and no supplement or exercise has been proven to restart it.
Growth Starts Before Birth
The penis begins forming around 8 weeks of gestation, when testosterone production ramps up in the developing fetus. Between weeks 8 and 21, male fetuses have peak levels of testosterone in their blood, which drives the formation of the internal structures, the urethra, and eventually the foreskin. By week 13, the core erectile tissues are already distinct and well-formed. This prenatal hormone exposure lays the foundation for the organ’s eventual adult size.
If testosterone levels are too low during this window, or if the body’s cells can’t respond to it properly, the result can be a micropenis at birth. In newborns, a stretched length under about 0.75 inches (1.9 cm) meets that clinical threshold, compared to an average newborn length of 1.4 inches (3.5 cm).
Puberty Is the Main Growth Phase
Most penile growth happens during puberty, which typically begins between ages 9 and 14. Testosterone floods the body as the testicles mature, and DHT, its more powerful derivative, directly stimulates the penis and scrotum to grow. A 2010 study found the average growth rate is less than half an inch per year from ages 11 to 15, then continues more slowly until around age 19.
Growth usually wraps up between 18 and 19, though some men see minor changes into their early 20s. After that point, the hormonal signals that drive tissue expansion have done their work, and no natural process will add further length or girth. For reference, a large analysis of over 15,000 men found the average erect penis is 5.1 inches long with a circumference of 4.5 inches.
Genetics Set the Range
Your DNA is the biggest factor determining where you land on the size spectrum. Two chromosomes play distinct roles. The X chromosome (inherited from your mother) carries the androgen receptor gene, which controls how many hormone receptors develop on penile tissue. More receptors means the tissue is more responsive to testosterone during puberty. Variations in this single gene can meaningfully affect final size.
The Y chromosome (inherited from your father) contains the gene responsible for forming the testicles in the first place. Testicle size influences how much testosterone gets produced during puberty, so this gene indirectly shapes growth as well. The interplay between these inherited factors is why penis size often, but not always, runs in families, and why there’s such natural variation between individuals.
Hormonal Treatment for Micropenis
For boys diagnosed with micropenis (a stretched length more than 2.5 standard deviations below average), testosterone therapy in infancy or early childhood can produce meaningful growth. Infants who receive treatment generally respond well, gaining adequate length and developing typical function as adults. The earlier treatment begins, the better the outcome tends to be.
This only works when the underlying cause is a hormone deficiency. In conditions where the body’s cells can’t respond to testosterone properly, such as androgen insensitivity syndrome, hormone therapy has little effect. In adults, a micropenis is defined as a stretched length of 2.67 inches (9.3 cm) or less, and hormonal treatment at that stage is far less effective than in childhood.
What Doesn’t Work: Supplements and Pills
No pill, powder, or supplement has been shown to increase penis size. The FDA maintains a running list of “male enhancement” products found to contain hidden, potentially dangerous pharmaceutical ingredients. These products are often marketed as natural dietary supplements with glowing online reviews, but the FDA classifies them as medication health fraud. Some have led to hospitalizations. The agency notes that its published list covers “only a small fraction” of contaminated products on the market, meaning the problem is far larger than what’s been formally flagged.
Herbal ingredients commonly found in these products (various root extracts, amino acids, and plant compounds) have no clinical evidence supporting penis enlargement. They cannot restart the hormonal growth process that ended in your late teens.
Surgical and Mechanical Options
Penile enhancement surgery exists but produces modest results. A review published in European Urology found these procedures typically add 1 to 2 centimeters in length (roughly half an inch to three-quarters of an inch) and about 2.5 centimeters in girth. Complications are common, including migration of injected filler materials and dissatisfaction with cosmetic outcomes. Most urological organizations do not recommend these procedures for men with average-sized penises.
Traction devices, which stretch the penis over extended periods, have stronger clinical backing, though the gains are still small. Clinical trials have reported increases ranging from 1.3 to 2.3 centimeters (about half an inch to just under an inch). Traditional devices require 2 to 9 hours of daily wear for months to achieve these results. Newer designs have shown similar benefits with 30 to 90 minutes of daily use, though much of this research has been conducted in men recovering from prostate surgery rather than in healthy volunteers seeking enlargement.
Why Size Changes With Age
While nothing makes the penis grow after puberty, several factors can make it appear or function differently over time. Weight gain adds a fat pad at the base that buries visible length. Reduced blood flow from cardiovascular disease, smoking, or diabetes can limit how firm and full erections become, making the penis seem smaller even though the tissue itself hasn’t changed. Maintaining cardiovascular health, a healthy weight, and good blood flow is the most evidence-based way to preserve the size and function you already have.