Smoking cannabis may cause early puberty and stunted growth in boys.
Scientists studied hormones in the blood of 437 boys, including 217 who habitually smoked cannabis before reaching puberty.
They found that levels of puberty-related hormones such as testosterone were raised in the drug users, who also had reduced levels of growth hormones.
By the age of 20, non-cannabis smokers were on average four kilograms heavier and 11.6cm taller than smokers.
The researchers also found that levels of the stress hormone cortisol were significantly higher in saliva samples from boys taking cannabis.