There’s a lot to unpack with that quote, and a full analysis requires us to consider the functions that opium served at the time Marx wrote. Asprin would not be invented for another 15 years after Marx died. Laudanum and morphine, both opiates, were extremely common pain-management tools of the era.

The full quote (supposing you like this particular translation), sheds some light on the context:

Religious suffering is, at one and the same time, the expression of real suffering and a protest against real suffering. Religion is the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people.

While I feel that the modern interpretation of (the snippet of) his quote is apropos, I think it’s also good to analyze what he was actually trying to say. These days I interpret Marx to be trying to essentially say “Religion serves as a painkiller for people exploited and/or alienated by a capitalist society.”

But I’m interested in hearing other perspectives, if you disagree!

Here’s some further reading on that particular quote. Bear in mind, I don’t necessarily agree with all the perspectives presented by them:

https://law.marquette.edu/facultyblog/2015/01/karl-marx-on-religion/comment-page-1/

https://en.wikipedia.org/wiki/Opium_of_the_people

https://cunninghamjeff.medium.com/karl-marx-was-a-capitalist-8a71138418fd#

https://www.firstthings.com/web-exclusives/2021/04/identity-politics-opium-of-the-people