I've never seen the phrase "chemically addictive" used by someone who knew what they were talking about. It's only used by people who don't understand that neurotransmitters are chemicals too. Stop spreading this BS distinction.
The most memorable withdrawal symptom from weed for me was the sweating. Cannabinoids tend to affect the hypothalamus which is sort of like the brain's control module for the endocrine system. And one of the things it controls is temperature regulation. So if you quit cold turkey that all gets outta wack and the sweating happens. Takes at least a couple of weeks to get somewhat back to normal.
Cessation of SSRIs can have all kinds of symptoms depending on the time length of usage, but I have never heard someone claim to be addicted to SSRIs.
Most people “addicted” wait much longer than that — sometimes months to make sure they have a strong trip and offset receptor down-regulation to the point where it can hardly be called an addiction.
Rapamycin isn't one I've heard of before, but it looks like a does-lots-of-things drug: Wikipedia says it's an immunosuppressant. I'd recommend against DIYing that for a different reason.
The doses used recreationally are multiples of what is regimen for anti-depressive effects.