Can Anastrozole or Letrozole Help Your Son Grow Taller?

By Kelli Davis, DO, and Toni Kim, MD, board-certified pediatric endocrinologists, LIFE Pediatric Endocrinology

Yes, for the right boy at the right time. Anastrozole (Arimidex) and letrozole (Femara) are aromatase inhibitors: small daily pills that slow the closing of the growth plates during puberty. In pooled studies, boys gained about 1 inch in final height on average, and the best individual results reached nearly 3 inches. Boys who also receive growth hormone can gain more.

Even an extra inch or two matters to a teenage boy. A 2-inch gain, a result within the range of the best trials but above the average, can be the difference between 5'7" and 5'9". That's why many parents ask us about these medications, often after being told to wait and see.

Our physicians bring more than 50 years of combined clinical experience, and we have prescribed aromatase inhibitors for more than 20 years. We start them when the timing is right in puberty, we continue them as long as they're helping, and we monitor every boy more closely than the traditional model does. This guide covers what the research shows, who is a good candidate, how anastrozole and letrozole differ, and how we keep treatment safe.

The short version:

• Aromatase inhibitors lower estrogen, the hormone that closes growth plates in boys as well as girls.
• Puberty and testosterone continue normally, so your son develops on the same timeline as his friends.
• The average gain is about 1 inch in final height, and the best results reach nearly 3 inches.
• The best results come from starting while bone age is still young, in early to mid puberty.
• Treatment is a daily pill, not an injection, but it needs regular labs and bone age X-rays to be done well.

How Aromatase Inhibitors Keep Growth Plates Open Longer

Estrogen, not testosterone, is the main signal that closes growth plates, even in boys. During puberty, an enzyme called aromatase converts some of a boy's testosterone into estrogen. As estrogen rises, the growth plates at the ends of the long bones mature and eventually fuse. Once they fuse, height growth stops.

An aromatase inhibitor blocks that conversion. Estrogen stays low, so the growth plates mature more slowly. Testosterone keeps doing its job: voice changes, muscle, body hair and the pubertal growth spurt all continue.

We track this with a bone age X-ray, a simple hand X-ray that shows how mature the skeleton is. On an aromatase inhibitor, bone age advances more slowly than the calendar does. In randomized trials, letrozole delayed bone maturation compared with placebo. Every month that bone age falls behind is extra time for growth.

This is the medical answer to the question many families type into Google: how to keep growth plates open. Sleep, nutrition and healthy weight all matter, but an aromatase inhibitor is the most direct tool we have during puberty.

How Much Taller? What the Research Shows

Pooled across studies, boys on an aromatase inhibitor finished about 1 inch taller on average, and the best individual trials reached nearly 3 inches. One meta-analysis of 14 studies found a final-height gain of about 2.5 cm (1 inch). The table below shows the key trials one by one, with whether each number was measured at adult height or predicted from a bone age.

Notice that duration matters. In the 2008 anastrozole trial, the predicted gain reached 6.7 cm in boys treated for three years. That's one reason we keep boys on treatment through puberty rather than stopping after a year.

We also want to be straight with you, because trust is the whole point of this article. The evidence is stronger for predicted height than for final height. A 2015 Cochrane review found that predicted height improved in every randomized trial, but it could not confirm a final-height gain because few trials followed boys to adulthood. In a Finnish follow-up of boys who were mostly prepubertal when they started letrozole alone, adult heights matched the placebo group. A 2024 Stanford trial concluded that an aromatase inhibitor alone may have limited benefit for some boys. Results depend on how short a child is, how young his bone age is when he starts, and whether growth hormone is part of the plan. Any physician who promises a specific number of inches is promising more than the science can.

Who Is a Good Candidate, and Why Timing Matters

An aromatase inhibitor works best for a boy who has started puberty, still has a young bone age, and is projected to finish shorter than his genetic potential. Your son does not need to be growth hormone deficient to benefit.

Boys we commonly evaluate for treatment include those with:

• A predicted adult height below his genetic target. Our child height calculator is a good first look.
• Short stature with no hormone deficiency, often called idiopathic short stature.
• Delayed puberty or constitutional growth delay.
• Fast puberty or a bone age running ahead of his real age, which shortens the growth window.
• Growth hormone treatment that needs more time to work before the growth plates close.

Timing is the single biggest factor you can control. A 2025 preprint that has not yet been peer reviewed found an average gain of 5.15 cm when letrozole began at a bone age of 14.5 or younger, compared with 2.58 cm when it began later. Starting well before puberty doesn't help much: in the Finnish follow-up, boys treated with letrozole alone while mostly prepubertal ended up the same height as boys on placebo. The window that matters is early-to-mid puberty.

That window is exactly when many families are told to wait and see. We disagree. Waiting a year in mid-puberty can mean losing the chance to treat at all. If your son is in puberty and you have questions about his height, the right time for a bone age and a full evaluation is now. Our puberty in boys guide explains the stages.

An aromatase inhibitor is not the right choice for every boy. If the growth plates are nearly closed, or if the evaluation shows a different cause of short stature, we'll tell you so and explain what will help instead.

Anastrozole vs. Letrozole: Which One?

Both work the same way, and in the one randomized head-to-head trial, neither produced a clearly taller final height. The difference is strength. Letrozole is the more powerful of the two, which affects hormone levels and growth speed.

In a three-year randomized trial at Stanford comparing the two, letrozole caused larger hormone swings and slower growth, and by the end the two groups had similar height outcomes (Journal of the Endocrine Society, 2024). A 2025 retrospective study of boys also on growth hormone found the best final heights in the anastrozole group, averaging 173.2 cm vs. 171.8 cm with letrozole (Journal of Clinical Endocrinology & Metabolism, 2025).

We choose based on your son's bone age, how fast puberty is moving, and his lab results, and we adjust as he grows. Some boys do well on one throughout; others switch. If your son starts anastrozole, our guide to foods to avoid when taking anastrozole covers diet and supplement questions.

It's a Pill. The Monitoring Is What Makes It Work.

Taking an aromatase inhibitor is easy: one small tablet a day, no injections. Doing it well takes close follow-up, and that is where LIFE is different. Many practices check labs only once or twice a year. We run labs every three months and track bone age throughout treatment.

Why it matters: lowering estrogen raises testosterone, sometimes higher than expected. Researchers at Children's Hospital Los Angeles warned that very high testosterone can push red blood cell counts up, which is why dose and labs need watching (MDedge). Studies have also flagged lower HDL ("good") cholesterol, higher uric acid, slower bone mineral gain, and mild changes in the shape of spine bones on X-ray in some boys. The long-term meaning of the spine changes isn't known, which is why bone health is part of our monitoring. These are manageable when someone is looking.

What we check, and how often:

If a number drifts, we adjust the dose, switch medications, or stop. Off-label use is common and appropriate in pediatrics, but it carries a responsibility to watch closely. We take that responsibility seriously.

The LIFE Approach: Medication Plus Everything Else That Drives Growth

A pill can protect the growth window. What fills that window is nutrition, sleep and a healthy body. We treat all of it in the same visit, and our physicians hold nutrition certifications so food is part of the medical plan, not an afterthought.

• Nutrition: enough protein, calories, calcium and vitamin D to build bone during the fastest growth of his life. Under-fueled boys, especially athletes, grow less.
• Healthy body composition: fat tissue contains aromatase and makes extra estrogen, so excess body fat can speed bone age. Helping a boy reach a healthy weight supports the medication.
• Sleep: most growth hormone is released during deep sleep. Teens need 8 to 10 hours.
• Activity and strength: weight-bearing exercise builds bone density, which matters while estrogen is lowered.
• Growth hormone when it fits: for some boys, combining growth hormone with an aromatase inhibitor gives the largest gains. We always discuss it openly. We also never prescribe it just because a family asks.

Every plan is built around your family's goals. Some families want to maximize every inch; others want reassurance and a clear picture. Both are good reasons to come in.

Find Out If Your Son Still Has Time to Grow

The growth window in puberty is short, and it doesn't reopen. A bone age X-ray and a full growth evaluation tell us how much time is left and whether an aromatase inhibitor could help.

LIFE is a national pediatric endocrinology practice. Families see our physicians by telehealth from anywhere in the country, and in person at our offices in Austin, Atlanta (Sandy Springs), Beverly Hills, Newport Beach and Nashville (Brentwood).

Schedule a growth evaluation with LIFE →

Frequently Asked Questions

Can anastrozole help my son grow taller?

Yes, anastrozole can make a boy taller if his growth plates are still open. Anastrozole lowers estrogen, which slows growth plate closure during puberty. In a randomized trial of boys on growth hormone, adding anastrozole raised predicted adult height by 6.7 cm (about 2.6 inches) over three years. That is a predicted height, not a measured adult height.

Can letrozole help my son grow taller?

Yes, letrozole can increase height in boys. In a small trial of 17 boys with delayed puberty, one year of letrozole alongside short-term testosterone led to an adult height about 6.9 cm (2.7 inches) taller than testosterone alone. Results are strongest when treatment starts early in puberty.

Is anastrozole or letrozole better for height?

Neither has been proven better for final height. Letrozole lowers estrogen more and slows bone age more, while anastrozole tends to keep growth speed higher. In a three-year randomized trial the two ended with similar heights, and in a 2025 retrospective study of boys also on growth hormone, anastrozole finished slightly taller. We choose based on your son's bone age, how fast puberty is moving, and his lab results.

How many inches can an aromatase inhibitor add?

Pooled studies show about 1 inch of extra final height on average, and the best individual trials reached nearly 3 inches. Adding growth hormone can add more: in a randomized trial, boys on both medications grew about 1.8 cm (0.7 inch) more than boys on growth hormone alone over 24 months. Many boys gain less than the best results. Bone age at the start, how short a boy is, and treatment length all affect the outcome.

Does my son need to be growth hormone deficient to qualify?

No. Many boys who benefit have normal growth hormone levels, including the boys in a 76-boy randomized trial. The key factors are a predicted height below his genetic potential and a bone age young enough to leave room to grow.

Will an aromatase inhibitor stop or delay puberty?

No. Testosterone continues to rise, so voice changes, muscle development and the growth spurt happen on time. Only the closing of the growth plates slows down.

What age should a boy start an aromatase inhibitor?

Early to mid puberty works best. In one preliminary analysis, boys who started at a bone age of 14.5 or younger gained about twice as much height as boys who started later. Starting well before puberty does little.

How long do boys stay on an aromatase inhibitor?

Usually through puberty, often until about 16 to 18, while bone age X-rays show remaining growth. Longer treatment was linked to larger gains in the research.

What are the side effects?

Many boys notice no difference day to day, and a Cochrane review of randomized trials found aromatase inhibitors were generally well tolerated. Lab effects can include higher testosterone and red blood cell counts, lower HDL cholesterol, higher uric acid and slower bone mineral gain. Some studies also found mild spine (vertebral) changes on X-ray, and their long-term significance isn't known. That's why we check labs every three months and follow bone health closely.

Do aromatase inhibitors build muscle?

Muscle isn't the goal of treatment, and research hasn't shown that an aromatase inhibitor builds muscle on its own. Testosterone rises on an aromatase inhibitor, but in a randomized trial of 76 boys, the extra lean mass appeared in the group that also received growth hormone. Another trial found that boys on letrozole had a lower percentage of body fat as their testosterone rose. In our practice, some active boys tell us they respond well to training during treatment, but we treat for height, not muscle.

Can my son play competitive sports while taking an aromatase inhibitor?

Yes, but competitive athletes need a plan. Anastrozole and letrozole are on the World Anti-Doping Agency (WADA) prohibited list, and the NCAA bans this drug class unless a medical exception is approved. If your son competes where drug testing happens, he'll need an approved exemption in advance, called a therapeutic use exemption (TUE) under WADA rules, and we help families with that paperwork.

Can an aromatase inhibitor reopen closed growth plates?

No. Once the growth plates fuse, no medication can reopen them. That's why evaluation during puberty matters.

Is an aromatase inhibitor FDA approved for height?

No, not for height. But aromatase inhibitors have been used and studied for growth in boys for more than 20 years, and our physicians have prescribed them for that long. Anastrozole and letrozole are FDA approved for other conditions, and pediatric endocrinologists prescribe them off-label for growth. Off-label use is common in pediatrics and should come with close monitoring.

About the Authors

Kelli Davis, DO is board-certified in pediatrics and pediatric endocrinology. She trained under Jill Simmons, MD, at Vanderbilt's Program for Pediatric Metabolic Bone Disorders, and her focus includes growth disorders and metabolic bone disease. That bone expertise shapes how LIFE protects bone health in every boy on an aromatase inhibitor. She sees families in person in Brentwood, Tennessee, and by telehealth.

Toni Kim, MD is the founder of LIFE Pediatric Endocrinology and a board-certified pediatric endocrinologist with more than 20 years of experience in growth and puberty care. She built LIFE's integrative approach, which pairs medications such as growth hormone and aromatase inhibitors with nutrition and lifestyle medicine. Before founding LIFE, she practiced in New York, and today she cares for families nationwide.

References

1. Mauras N, Ross JL, Gagliardi P, et al. Randomized trial of aromatase inhibitors, growth hormone, or combination in pubertal boys with idiopathic short stature. J Clin Endocrinol Metab. 2016;101(12):4984-4993.
2. Mauras N, et al. Anastrozole increases predicted adult height of short adolescent males treated with growth hormone: a randomized, placebo-controlled, multicenter trial for one to three years. J Clin Endocrinol Metab. 2008.
3. Wit JM. Aromatase inhibitors in paediatric endocrinology (review of the Hero, Wickman and Salehpour trials). J Clin Res Pediatr Endocrinol. 2015;7(Suppl 1).
4. Hero M. Doctoral thesis on letrozole treatment in boys with short stature and delayed puberty, summarizing the randomized letrozole trials. CORE repository.
5. Aromatase inhibitor effectiveness on height augmentation: optimizing letrozole therapy for height gain in short-statured boys. Research Square preprint, not peer reviewed. 2025.
6. Anastrozole vs letrozole to augment height in pubertal males with idiopathic short stature: a 3-year randomized trial. J Endocr Soc. 2024;8(10):bvae141.
7. Cui Y, Zhang Q, Hou L, Luo X. The combination of aromatase inhibitors and GH treatment for idiopathic short stature in male adolescents. J Clin Endocrinol Metab. 2025.
8. Kerttula L, Dunkel L, Hero M. Letrozole monotherapy in pre- and early-pubertal boys does not increase adult height. Front Endocrinol. 2019;10:201.
9. High testosterone, no growth benefit for boys treated with letrozole. Clinical Endocrinology News (MDedge).
10. Efficacy of letrozole combined with recombinant human growth hormone in boys aged ≥10 years with advanced bone age and impaired growth potential. Front Endocrinol. 2026.
11. McGrath N, O'Grady MJ. Aromatase inhibitors for short stature in male children and adolescents. Cochrane Database Syst Rev. 2015, Issue 10.
12. Aromatase inhibitors for idiopathic short stature: a commentary (summarizes a meta-analysis of 14 studies). J Pediatr Endocrinol Diabetes.
13. World Anti-Doping Agency. Prohibited List, section S4, hormone and metabolic modulators (aromatase inhibitors).
14. Wickerham DL. Oncologist details antiestrogen ban. The NCAA News. 2007.

Medical Disclaimer

This article is for general education and is not medical advice. Anastrozole and letrozole are not FDA approved to increase height; their use for growth is off-label and requires evaluation and ongoing monitoring by a qualified pediatric endocrinologist. Study results describe groups of patients, and individual results vary. Talk with your child's physician before starting, stopping or changing any medication.