Binge drinking stunts the growth of teenagers' brains, according to new research.
Experiments on adolescent monkeys found heavy exposure to alcohol reduced the development of both grey and white matter.
Scientists believe the same will apply to humans - and could affect their ability to learn.
Every gram of alcohol consumed per kilogram of body weight lessened growth of the animals' neurons by 0.25 milliliters per year.
In human terms that is the equivalent of four beers per day, according to the new study.
Experiments on adolescent monkeys found heavy exposure to alcohol reduced the development of both grey and white matter, Oregon Health and Science University found
Lead author Dr Tatiana Shnitko, of the primate research center at Oregon Health and Science University, said alcohol abuse is particularly dangerous in adolescence.
'This is the age range when the brain is being fine-tuned to fit adult responsibilities,' Dr Shnitko said.
'The question is, does alcohol exposure during this age range alter the lifetime learning ability of individuals?'
The study published in eNeuro found heavy drinking on the 'cusp of adulthood' slowed up brain growth in the male and female rhesus monkeys.
It could inform future investigations into how these changes may influence problematic drinking in humans later in life.
Previous research in humans and rodents had already established a link between excessive drinking and reduced brain volume.
Now Dr Shnitko and colleagues - supported by the National Institute on Alcohol Abuse and Alcoholism - have extended these findings.
The first long-term trial of its kind using a non-human primate model showed how voluntary intake of alcohol in late adolescence and early adulthood affects brain development.
Monkeys characterized as heavy drinkers based on their consumption and blood samples suffered dramatic reductions in brain growth.
In particular this was their white matter which helps neurons to communicate and the thalamus - a walnut-sized region of grey matter that relays sensory and motor information.
The researchers examined the brains of