Today's linguistics lesson is about how words change in meaning from the specific to the general, and back again.
The word "dope" has cognates in the other Germanic languages, and is probably related to the word "daub." In the early 1800's, it referred to the thick concentrated opium goo imported from Asia. It gradually acquired forms such as doped, doped up, dopey referring to the condition of being on opium and eventually, having the appearance of being on opium. This broadened further to include being under the influence of any drug. It still held this meaning until the 50's and even 60's. It is still used by people complaining about the psychiatric profession complaining that their friends or relatives who are slowed down look "doped up." But as marijuana became the most commonly used drug, the word dope began to gravitate primarily to that substance.
The slang has changed, and saying dope instead of pot or weed now has an archaic flavor. When the word is used at all, it is becoming general again.