As I understand it (not being a biology major) they set off switches that make the brain go "more, more!'. This is not just restricted to drugs we stick in ourselves; it's how the machine works. Chemicals go in, other chemicals get blocked, receptors ping (or dont ping), more nerves fire off (or stop firing off), more chemicals get made to repeat the cycle somewhere else, or they don't get made and other chemicals start doing funky stuff themselves.
For example, caffeine: works by sitting on top of a receptor perfectly, but without the necessary bit to flick that receptor on. Like a key that's got the perfect set of teeth, but missing the sole necessary one to open the lock. As long as we have that receptor for the purpose of {whatever exactly is its job, but in general telling us to sleep} then caffeine will have the effect of blocking that receptor and prevent it doing its job.
From the natural standpoint: it's not something that really can be turned off. We physically cannot lose the ability to flip switches with drugs for as long as we have switches. Since those switches are a necessary part of the body, we will always have those switches.
From a technological standpoint: it's possible that one day we could get implanted with circuits and electronic gizmos to do stuff for us, to regulate a little more effectively or to make the controls.. controllable.
But at the end of the day, those fancy chips and doodahs are doing the exact same job that the receptors do now. They will necessarily run on similar pathways (e.g. measuring levels of stuff, having places which are/are not activated by certain chemicals) and so they will be susceptible to the same interruptive or accelerative effects we endure now.
As long as there are switches to be flipped and a brain that likes them flipped, we will use drugs.
Unless somebody figures out how to put a limiter on those switches. You'd make millions out of being able to stop addiction with a
simple pretty frickin' complicated surgery or to turn hormones and glands on and off with a push of the remote.
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