This claim came from a reporting from New York Times. Both CBS and X make this assertion, but based on information and citations from the NYT article. In this article, it is never clearly stated that Musk "has been abusing ketamine and other drugs since campaigning with Trump." The Times article asserts that Musk was using drugs when he joined Trump's campaign, which is backed by some evidence, but never clearly claims that Musk has been using drugs ever since. In fact, the NYT article admits that "It is unclear whether Musk, 53, was taking drugs when he became a fixture at the White House this year." So while it may certainly be true that Musk had been taking drugs in the past, particularly at the beginning of the Trump campaign, it is only mere speculation that Musk has continued his drug habit. Musk has admitted using drugs in his past, so this was no revelation. The Times discusses circumstances, such as Musk's "erratic behavior" and interesting lifestyle choices, that may suggest evidence of continued drug usage. Yet, this is only hypotheses and speculation. Even Musk's request to "move on" from questions by the NYT concerning his drug habits is not evidence enough that he is currently engaging in such.
https://www.nytimes.com/2025/05/30/us/elon-musk-drugs-children-trump.html
Another article, written by the Guardian, states that it "remains unclear whether Musk was under the influence during his time at the White House." This article, along with others that I looked into (including CBS, CNBC) reported on evidence of Musk's past drug use and poor lifestyle choices. Words like "reportedly" and comments regarding Musk's actions from "last year" are commonly found. They similarly suggest that Musk very well could be using drugs now, but there is no concrete evidence of this. No source has been able to confirm anything that was reported in the original NYT article, either.
https://www.theguardian.com/us-news/2025/may/30/elon-musk-trump-drug-use
https://www.cbsnews.com/news/elon-musk-lashes-out-in-oval-office-when-asked-about-report-on-his-ketamine-use/
https://www.cnbc.com/2025/05/30/elon-musk-drugs-trump-.html
From my perspective, these articles latched onto Musk's refusal to answer questions about his drug habits and drastically expanded on his past. They took a controversial and clickbait-y headline to create a bit of drama and make suggestions that are, at this point, impossible to prove one way or the other. There is simply no scientific report or admissions made by Musk that tell us he has been using drugs ever "since campaigning with Trump." What is true of his past is not necessarily true of the present. This claim is both misleading and based on limited, non-concrete evidence.