Being under the influence of a controlled substance is a violation of California Health and Safety Code 11550(a).

Being under the influence of cocaine would be a violation of this section. Being under the influence "a couple weeks ago" would not be.

If I was a cop driving around, and you walked up to me and said "hey, I'm high out of my mind on coke." I'd probably look at you for a second and see if there were any factors to corroborate that. Pupils, rapid speech, sweating, (weather appropriate?) fidgeting, etc. Cocaine is a stimulant, are you displaying symptomologies consistent with that?

I may then conduct a 7-step DAR or 12-step DRE evaluation (based on my level of training.) If I determine you're under the influence, I'm going to arrest you. I'm then going to obtain a urine sample and test it. We used to be able to do forced blood draws for 11550's in CA. Thanks US Supreme Court...

Basically even if you tell on yourself, unless there is substantial evidence that you are actively stoned you are okay.

Another way to think about it is this:

The DEA has a sizeable but limited budget. They would rather take out traffickers and cartel guys than writers who could make a good case out of first amendment protections. Even if there weren't huge constitutional issues, they still have to prove that the claims written about were factual and not fabricated. This kind of investigation would take a lot of money, and for the money they spent they would be able to make a bigger impact somewhere else.

https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC&sectionNum=11550

(I found this all out while researching Terrence McKenna and thinking of publishing my own trip logs and inebriated recollections)

(This is my first time answering a question on this sub I really hope this is helpful and appropriate.)