Does Weed Stunt Your Growth?

Smoke weed and you will stay short. Teenagers have heard some version of that warning for decades, and it has a scientific hook, since cannabis acts on the same hormone system that drives growth.

The evidence in actual people is much thinner than the warning, and the better-documented risks for teens lie somewhere else.

Key takeaways

• Height is mostly inherited, and growth stops once the bones' growth plates fuse, usually in the mid-teens for girls and late teens for boys.
• In rats, THC slowed the pubertal growth spurt, and in mice it slowed bone lengthening through the CB1 receptor.
• Six men given very high oral doses of THC for two weeks in 1976 showed a weaker growth hormone response.
• The only human comparison of teen users' height is a 2015 conference abstract from Pakistan, not a peer-reviewed paper.
• Cannabis use in pregnancy is linked to lower birth weight, but a 2016 meta-analysis found no effect on birth length.
• For teens, psychosis risk and dependence are better-documented concerns than height.
• After the growth plates fuse, no study suggests cannabis changes adult height.

How height is decided

Any question about weed and height starts with how height works. Genes do most of the work, and twin studies put the heritability of height at 60% to 80%. Nutrition and health shape the rest.

Growth happens at the growth plates, layers of cartilage near the ends of the long bones. Rising estrogen in puberty, in boys as well as girls, closes them for good, and complete fusion can occur as early as 12 for girls, though 14 to 15 is most common, and as early as 14 for boys, most often at 15 to 17. The average timeline looks like this:

Growth hormone, made in the pituitary gland, drives the process together with IGF-1, which the liver produces in response. Its biggest daily pulse comes about an hour after falling asleep, during deep sleep, and sleep deprivation generally suppresses its release.

Cannabis and growth hormone

Most of what is known about cannabis and growth hormone comes from animals. The link is plausible on paper, because the CB1 receptor that THC switches on is found in the hypothalamus and the pituitary gland, the brain's hormone control center.

Rats and mice

In a 1983 rat study, THC given every other day to young males from day 16 to day 87 resulted in a significant decrease in pubertal growth spurts, especially the second peak. Testosterone and other sex hormones fell too. When the drug was stopped early, the rats' body growth caught up, even though testosterone stayed low.

In a 2015 mouse study, THC slowed the lengthening of the thigh bone and spine in female mice through the CB1 receptor, which left them lighter. The authors wrote that the relevance of their findings to humans remains to be studied.

Adult volunteers and sleep

Human data are scarce. In a 1976 study, six hospitalized men took 210 mg of oral THC a day for two weeks, many times a typical dose, and their peak growth hormone response to an insulin test fell from an average of 52.6 to 18.8 ng/ml. The authors read it as suppression of the brain's hormone axis after prolonged high-dose use. They did not measure growth, and the men were adults.

Sleep is the other route people worry about, since growth hormone peaks in deep sleep. Early studies found that acute THC increased slow-wave sleep and cut REM sleep, and Barney's Farm's own sleep research roundup notes that THC tends to increase deep sleep while reducing REM. Regular users build tolerance, though, and withdrawal disrupts sleep. We found no study that measured growth hormone through that cycle.

Bone density in adults

Bone strength is a separate question from height, but it comes up in the same searches. A UK study of 144 heavy users, people with more than 5,000 lifetime smoking sessions, found lower hip and spine bone density and about twice the fracture rate of 114 cigarette smokers, partly because the heavy users weighed less. A US survey of 4,743 adults aged 20 to 59 found no link between cannabis and bone density at any level of use.

Teens, weed and growth in human studies

For teens, weed and growth have been compared directly only once in the research we found. At a 2015 European endocrinology meeting, researchers from Pakistan presented data on 437 boys, 220 non-smokers and 217 described as marijuana addicted, and reported that the non-smoking boys were 4 kg heavier and 4.6 inches taller than addict boys at the age of 20 years. Growth hormone was higher in the non-smokers during puberty, while testosterone, LH and cortisol were higher in the users, and the authors suggested that marijuana may speed up puberty and suppress growth.

That result comes with heavy caveats:

• This is a conference abstract, and we found no full peer-reviewed paper behind it.
• The design compares two groups at one point in time and does not follow them over years.
• Its title says the boys smoked marijuana in cigarettes, so tobacco was part of the exposure.
• No details are given on how the boys were recruited or what else differed between the groups.

Tobacco alone is linked to shorter teens. A 2008 Canadian study of 1,293 Montreal teens estimated that a boy who smokes 10 cigarettes a day from age 12 to 17 ends up about an inch shorter than a boy who does not smoke.

So does weed stunt your growth? The research allows a cautious answer: it might, through hormones, during puberty, but no well-designed human study has shown it.

The unexamined day is a wasted opportunity. Reflect on what you did, what you learned, and how you can improve.

John Dewey

Before birth, weight and not length

Pregnancy is the one setting where growth has been measured carefully. A 2016 meta-analysis of 24 studies in BMJ Open found that infants exposed to cannabis in utero had a decrease in birth weight, along with other differences:

• About 109 grams lower birth weight on average
• Higher odds of low birth weight
• About twice the odds of neonatal intensive care
• No difference in birth length or head size

The authors could not separate cannabis from the tobacco and alcohol that many users also take.

Adults past their growth years

So does weed make you shorter once you are an adult? Nothing in the research says so. Once the growth plates have fused, bones stop getting longer, so there is nothing left for cannabis to stunt, and the open question for adults is bone density, not height.

In our experience, the only height question grown-ups can still control is in the grow room. MAC 1, an Alien Cookies and Miracle 15 cross at 27% THC, can reach 180 to 250 cm outdoors, while Watermelon Z Auto, a Watermelon Z and BF Super Auto #1 cross at 26% THC, tops out around 140 cm outdoors and 110 cm indoors, which suits a balcony or a small tent.

Bigger teen risks than height

Height is the wrong worry for most teens. In an Ontario study of 11,363 young people tracked through health records, cannabis use was significantly associated with psychotic disorders during adolescence, at about 11 times the risk, but not during young adulthood. Cannabis dependence develops in about 9% of users, with young and frequent users at the most risk. A 2021 study of 799 European teens scanned at 14 and again around 19 found that the more cannabis they used, the faster part of the prefrontal cortex thinned, though the study could not prove that cannabis caused it.

Most teens do not use it at all. In the 2025 Monitoring the Future survey, 8% of eighth graders, 16% of tenth graders and 26% of twelfth graders reported using cannabis in the past year, and 2%, 6% and 9% used hemp-derived products such as delta-8.

Growth plates, hormones and the real risks

Weed has not been shown to stunt growth in people. THC slowed the growth spurt in rats and bone lengthening in mice, high oral doses blunted growth hormone in six adult men, and the one comparison of teen users' height comes from a conference abstract tangled up with tobacco. Before birth, cannabis is tied to lower weight, not shorter length. For teens, the stronger reasons to wait are psychosis risk and dependence, and once growth plates fuse, height is settled.

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