[Alupis]

You can refill them. They typically have a plastic plug on one side, and some companies will refill them for you, or you can buy a refill "kit".

However, the internals of the cartridge will break down over time. Typically it's the "blade" that evens out the powdered toner that wears out, leaving too much toner stuck to the page and results in those gray-page prints and streaks/lines.

If you buy refilled cartridges, the blade seems to be the most common failure point long before you run out of toner.