Is using generic toner detrimental to laser printers?

Printer manufacturers usually recommend that you only use their branded, OEM toner cartridges in their products but generic ones are commonly available for far less cost.

Print quality will of course vary between different brands/makes/models and personal experiences, so that discussion is one of opinion, however:

Does using generic toner cause any damage, or otherwise have any negative effect on the printer's lifespan? I'm struggling to find any unbiased studies.

There is a similar but different question on ink/toner refill kits here, but I'm referring to generic already-filled cartridges that can be bought online or in some discount stores.

While I would be inclined to use after market cartridges as they are much cheaper then originals, and printers are generally cheap relative to the costs of consumables, not all after market cartridges are equal and the quality is not always as good as the originals.

I believe that "Which" in the UK is a Consumer funded organization. This article talks about replacement ink cartriges, and has a useful table on the their users experiences. In summary, 63% of users had no problems, about 35% had problems related to print quality, 3% complained of ink spillage and 10% complained of other problems. (I have no idea why these figures add up to > 100% !!!). If you happen to be in the UK the article is also useful as to investigating your rights as a consumer.

A report (requires subscription) on printer reliability from the prominent Consumer Supported testing company in New Zealand found that 25% of the people they sampled had problems with generic cartridges compared with 6% of those who used same-brand cartridges.

In New Zealand we have strong protection laws, and the laws prohibit manufacturers from denying warranty claims if you use compatible consumables where the consumables were not likely the cause of the problem. You might want to look at your local laws and be guided somewhat by whether you have statutory protections.

Based on 25 years of feeding the things:

Other than quality or lack thereof (which does vary quite a bit) no, there is no magic sauce from name-brand cartridges just due to the name brand (for which a significant premium is charged.) In the used market you can pick up a whole spare printer for the savings on a couple of cartridges if you don't need the latest laser printer they make.

I have never had "printer damage" from crappy cartridges - low print quality, short useful life of a cartridge, and sometimes leaking toner to remove, but no actual damage. Purported damage is a scare tactic to protect the high profit margins on replacement toner. Laser printer damage (in my experience over 25 years) comes from poor packing and shipping, users putting things that don't belong in printers in printers, and poorly engineered "new and improved" (not) fusers that self-destruct.