I'm in an HMO - if I had a medication problem I'd need to visit urgent care to see an MD or an ER when it is after hours. There is an emergency number to call to get instructions or if you are in immediate danger of harm, but again it's a central HMO number not tied to my pDoc.

For therapist after hours? Leave a VM or email. Get answer during business hours.
So, I've used my other lifelines - forums, friends, family, etc.

It's good to know what the choices are, and sometimes you will have to choose something that is not ideal (such as going to the ER for a "medication problem". it may seem like overkill?) in order to get appropriate care.
But the most important thing is to take care of yourself, even if it's not ideal.