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There is a general consensus that higher brain functions, and so, ultimately, behaviour, are controlled by dynamic communication at the synapses that connect neurons. Decades of psychopharmacology studies have validated this view, because most psychoactive drugs seem to exert their effects on mood and behaviour by interfering with the function of chemicals called neurotransmitters at synapses1. This mechanism is proposed to mediate behavioural responses to compounds called cannabinoids1, which are the active ingredient of marijuana. But writing in Nature, Jimenez-Blasco et al.2 report a different mechanism of action for the cannabinoid tetrahydrocannabinol (THC) that involves the metabolism of lactate molecules in non-neuronal cells called astrocytes. This discovery cautions against an oversimplistic view of the mechanisms that underlie behaviour.