The Hippocampus Argument
In a certain kind of Berlin apartment in 2013, smoking weed was roughly as remarkable as making coffee—Club Mate in the fridge, a pirated series buffering in another window, a joint making its rounds. The news that Kreuzberg might host Germany’s first legal cannabis shop landed, in those circles, somewhere between obvious progress and a collective shrug.
But there’s another argument, and it deserves more than a dismissal. Julia Völker interviewed psychiatrist Rainer Thomasius—head of the German Center for Addiction Issues in Children and Adolescents at Hamburg-Eppendorf University Hospital—for ZEIT ONLINE, and his position is unambiguous. Cannabis can permanently alter the brain,
he says. In adolescents, brain changes last a lifetime—a reduction in the size of the hippocampus, which contains important memory structures.
Five percent of his young patients arrive with psychotic symptoms. In some, a full schizophrenia is triggered by the drug.
The standard counterargument—that legalizing for adults doesn’t mean access for minors—doesn’t satisfy him. The symbolic signal is the problem. Legalization normalizes. There is no safe consumption during childhood and adolescence,
he says. These young people haven’t developed their own personalities yet. They’re deeply insecure, really just looking for closeness and security.
Treatment numbers are rising, he notes, but services only reach a fraction of those who need them.
Julia also spoke with an 18-year-old who had been living with cannabis addiction for years. His account has the familiar shape: the first joint that made him wonder why adults had been lying to him about something so harmless, then the slow escalation—half a gram a day becoming five, six hundred euros a month, the high eventually evaporating until he needed the drug just to feel normal enough to leave the house. School dropped. Kicked out by his parents. I knew I wanted to stop. But I couldn’t do it alone.
Therapy, eventually. That’s where the story ends for now.
None of this settles the argument for prohibition. Adults making autonomous choices about their bodies is a different question from whether teenagers end up with access, and the evidence from places where legalization has already happened doesn’t show mass youth addiction spikes. The hippocampus concern is real, but it’s the kind of argument that could be made—and was—against alcohol, caffeine, anything that touches mood or perception.
What stays with me is his description of the moment when the drug stopped functioning as a pleasure and became a requirement for normal. That flipped switch—when a substance stops being something you want and becomes something you need just to exist at baseline—that’s the part no policy framework fully addresses. Adults get there too. But the younger you are when it happens, the longer you live inside it.