Drugs, specifically stimulants.
Dex Term Timeline in Neuromancer
The timeline below shows where the term Dex appears in Neuromancer. The colored dots and icons indicate which themes are associated with that appearance.
...Armitage. Case takes Molly to the Chat, and when he takes out an octagon of dex, she informs him that his new pancreas and the plugs in his liver will prevent... (full context)