How do you know if your coworker could possibly be on drugs

There could be a number of medical issues. If she isn’t your direct report, let her person know in a kind way. We never know the battles others are fighting.

Some medications, vitamin deficiencies, and health conditions cause stuff like that.

How old is she?

This could be from stress or other problems in their personal life including a change in or new medications, minor head trauma or injury (a head injury from a fall or accident), emotional disorders. stress, anxiety or depression, alcohol or drugs,
Vitamin B-12 deficiency, brain diseases, a tumor or infection in the brain, sleep Apnea, and a lot of other things not obvious to the passerby/coworker.

Really, the best thing would be to talk to her in private... you know, pick the moment kind of thing.

you don't know, unless they want you to know. is this individual older?

How old is your co worker if over 40 could be signs of dementia also sometimes brain tumors cause this if they havent been to a doctor.

You could try the old “the lady doth protest too much, methinks” drug test. In a humorous sort of way say something like – How could you not follow those simple instructions – are you on drugs? If the person says no and then starts given you 1001 reasons to try and prove their not on drugs - then maybe they are on drugs. You could also say something like – what do you think of the new random drug test policy – if the person gets a terrified look on their face – they might be on drugs. Cheers!

Is she getting enough rest? Are things ok at home?

It could be a new medication or health issue. I was that way the first few weeks of starting Prozac.

Sounds medical. Reminds me of my grandmother when her dementia started progressing.

Some just outright tell me.

Doesn’t your work place have drug testing, if so why do you care , if she’s showing up doing her work, and they haven’t tested her it’s none of your business

It seems she has some medical problems or may be side effects of some medication. Or early sign of dementia.
Liver problem can affect that way too.
Drug problem has other signs too.

Maybe she doesn't want to talk.

Intense stress will also do that.

She could have a medical issues. You could just ask her if she’s okay, you have noticed some changes and you were wondering if she needed help?

More likely they aren't on anything and that's the problem.

Casually approach the coworker during a lunch break or other break and say something subtle, like, "Boy, some drugs would sure hit the spot. I sure wish I knew someone who could get some." See what your coworker says.