On Friday, Twitter users began noticing that the service was blocking search results for “marijuana,” “cannabis” and other drug-related terms.

The change appears to be part of a new “sensitive content filter” that Twitter is rolling out to users and is turing on by default, without notice.

hi @Twitter! I'm a journalist. Why the fuck are you censoring my ability to search for tweets abt the topic I cover? https://t.co/dr0gjLpSbX — Amanda Chicago Lewis (@msamandalewis) March 27, 2017

Update: Twitter now blocking real-time search results for LSD & other drug-related terms behind new "safe search" feature. [via @erowid] pic.twitter.com/69QObj0NOG — Heads News (@HeadsNews) March 26, 2017

Nonetheless, Twitter isn’t blocking searches for opioid-related terms. As the Washington Post’s Chris Ingraham pointed out, queries for “buy vicodin” continue to generate lots of visible results.

.@Twitter is censoring real-time results for "cannabis," but not for sketchy businesses purporting to sell opioids without a prescription pic.twitter.com/EiEEVFB3es — Christopher Ingraham (@_cingraham) March 26, 2017

A change.org petition pushing Twitter to stop censoring marijuana results argues:

“Twitter is a platform that many activists use to spread information about important policy issues like marijuana legalization and medical cannabis. Journalists use Twitter to research stories and stay up to date on developments. And elected officials use Twitter to keep their finger on the pulse of what their constituents care about… Censoring marijuana-related searches prevents serious people from communicating about one of the most prominent policy issues of our time.”

(Full disclosure: The petition was uploaded by the activist group Marijuana Majority, which was founded by the author of this article.)

The settings to turn off the sensitive content filter cannot be accessed using Twitter’s iOS app or its TweetDeck platform. On the web, the option can be found on the search results page:

The new filter isn’t just blocking drug terms, either. Searches for several sex-related and anatomical keywords are now censored, too, as are queries for seemingly innocuous words like “pick” and “pipe.”

I'm searching for PIPE (Private Investment in Public Equity) deals, but apparently Twitter thinks I'm looking for drug paraphernalia. — Elie Litvin (@ElieLitvin) March 26, 2017

A filmmaker was surprised to find that the name of her new movie, “Red Pill” was returning zero results.

Something's weird. Can you all do me a favor & search "red pill" & "red pill movie" on Twitter & see if there's anything under latest &news? pic.twitter.com/IqfFDEygoW — Cassie Jaye (@Cassie_Jaye) March 25, 2017

It is unclear why Twitter would turn the content blocking setting on automatically for users without notification, or why marijuana-related terms would be marked as sensitive while opioid-related searches are not.

The “sensitive” words are blocked from generating results under Twitter’s search tabs for Latest, News, People, Photos and Videos tabs, but for some reason still show up under the Top and Periscopes sections.

The move appears to be part of a wider effort to stop abuse and trolling on the service, though it has not been without snags. Entire profiles — including that of a prominent technology analyst — have been marked as sensitive.

Twitter support staff and CEO Jack Dorsey did not respond to MassRoots’s requests for comment.