Does Smoking Weed Really Stunt Your Growth? The Evidence

Does Smoking Weed Stunt Your Growth?

This is a common concern, especially among teenagers and young adults who are still growing. Marijuana contains tetrahydrocannabinol (THC), the psychoactive component that produces the high associated with weed. THC interacts with the body's endocannabinoid system, which regulates various functions including appetite, pain perception, mood, and memory. This system also plays a role in proper growth and development.

During adolescence, the endocannabinoid system is actively maturing. Some research indicates that regular marijuana use during this critical developmental window may disrupt normal endocannabinoid signaling, potentially impacting growth and brain development. However, the evidence is still limited and findings have been mixed.

Animal Studies on Weed and Growth

Most of the evidence on the effects of marijuana on growth comes from animal studies. These types of studies allow researchers to control for factors like age of exposure, dosage amounts, and duration of use. However, animal study results do not always translate perfectly to humans.

Animal studies have found that exposing adolescent animals, like rats or mice, to THC can alter endocannabinoid signaling in the brain and cause decreases in body weight and length compared to non-exposed controls. The animals exposed to THC also tended to have decreased fertility, particularly among females.

For example, a 2015 study published in Scientific Reports gave young mice a synthetic cannabinoid compound every day for 3 weeks. The mice exhibited reductions in body length, weight, liver weight, and bone mineral density compared to mice not given the cannabinoid.^[1]

Another study from 2003 found that rats exposed to THC during adolescence and adulthood ended up shorter than control rats and had decreased bone mineral content as adults. The effects were more pronounced in female than male rats.^[2]

Based on this type of research, the general conclusion is that regular marijuana use early in life may alter the endocannabinoid system and growth regulation in animals. But animals are not perfect proxies for humans.

Human Research on Marijuana and Growth

In humans, marijuanas impacts on growth are more difficult to study. There are fewer controlled trials, and many rely on self-reported data, which can be unreliable. Overall, human research has not found a definitive link between cannabis use and stunted growth.

A well-known long-term study trackedHeight and weight measurements of over 10,000 people throughout adolescence and adulthood. Marijuana users tended to be shorter and weigh less than non-users.^[3]

However, this study relied on self-reported marijuana use. It also did not account for variables like socioeconomic status, nutrition, genetics, or other drug use. So, it cannot prove that marijuana directly caused reductions in height or weight.

A 2019 longitudinal study measured growth annually in a group of teenagers from ages 13-19. There were 79 regular marijuana users and 146 non-users. On average, the marijuana users were no shorter than non-users. The users were slightly thinner on average, even when accounting for other drug use.^[4]

Interestingly, another study tracked brain development and IQ in teenagers who used marijuana daily for 3 years. Their growth rate was normal throughout the 3 years with no increased risk of stunted growth.^[5] So chronically high exposure did not seem to impact their height.

Overall, results are mixed and human studies have not conclusively established that marijuana use causes clinically significant reductions in growth or height in humans, especially when accounting for other factors. More large-scale longitudinal research is still needed.

Possible Reasons Why Weed May Not Stunt Growth

There are several reasons why marijuana may not actually alter growth trajectories in humans to the extent expected based on animal studies:

• Humans have a longer adolescent developmental period so there is more time to catch up from any delays induced by weed.
• Humans use much lower doses of weed than given to animals in controlled experiments.
• Humans do not use weed as consistently or start as early as animal studies.
• Preclinical studies often only look at body weight and length, which are just two measures of growth. Weed may not impact long bone elongation that determines height.

Genetics and nutrition status are also strong determinants of growth and may override or mitigate any small effects of marijuana use. Finally, most human studies rely on self-reported marijuana use, which is often underestimated. This makes it even more difficult to detect small changes in growth due to weed.

Risks are Higher with Early Use

While the impacts on physical growth are unclear, early marijuana use has been associated with cognitive impairment and increased risk of drug abuse or addiction later in life.^[6]

During adolescence, the endocannabinoid system, prefrontal cortex, and other areas of the brain are still developing. THC interacts with CB1 receptors concentrated in these regions. Early chronic use may rewire reward pathways at a vulnerable time.

Using marijuana frequently in adolescence is linked to poorer cognitive performance, reduced motivation, increased impulsivity, and increased risk of psychiatric disorders like anxiety or depression later on.^[7]

The brain and cognitive effects are most pronounced in teens who start around age 14 or younger.^[8] For optimal brain maturation, it is best to avoid recreational marijuana use during adolescence.

Quitting Marijuana May Reverse Effects

The majority of human research has not found strong evidence for marijuana stunting growth permanently or irreversibly. However, early chronic use may delay growth and pubertal development slightly.

Fortunately, these effects seem to reverse after stopping marijuana use. In one study, teenagers who quit using marijuana increased their expected adult height projections over time to match non-using peers.^[9]

For teens and young adults who are still growing, quitting marijuana will likely allow growth to proceed normally. However, the cognitive effects of early chronic use may be longer-lasting.

Other Factors Impact Growth More

While more research is warranted, the bulk of current human studies indicate marijuana itself has relatively small, transient effects on physical growth, if any. Genetics, nutrition, and lifestyle factors appear to be much more important determinants of height and growth trajectory.

For example, deficits of growth hormone, thyroid hormone, sex steroids, and proper childhood nutrition can dramatically reduce height potential. Growth hormone deficiency alone can result in final heights 7-15 cm shorter than expected.^[10]

Likewise, secondhand smoke exposure in childhood, lack of exercise, mental health issues, inadequate sleep, and substance abuse involving alcohol, opioids, or other drugs seem to influence growth and height potential to a greater degree than marijuana use alone.

Teens worried about maximizing their growth should prioritize proper nutrition, sleep, exercise, and minimizing use of all substances until the brain and body have fully matured.

The Bottom Line

Based on current evidence, occasional or moderate marijuana use is unlikely to stunt growth or final adult height drastically. Heavy, chronic use starting at very young ages may modestly delay growth but these effects seem to reverse with abstinence.

However, marijuana impacts brain development, cognition, and mental health more clearly. Frequent use during adolescence is not recommended for brain and mental health reasons. While more research is needed, focusing on healthy lifestyle choices appears most important for achieving full growth and height potential.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.