Dreams are expressions of your feelings about what's most important to you in your waking life. The language of dreams does not change when you dream, although your feelings about the waking life catalyst for the dream might be affected, just as they can be in waking life by drugs or other mood altering substances.
Here is a relevant Q&A I found in the FAQs on this site...
"Q. Can a person affect what they dream about by food, drugs, or alcohol? Or by any other method?
A. Some people say pineapple pizza and chocolate gives them wild dreams, but no one has really been able to prove this! Most drugs—sleeping pills, marijuana, alcohol—decrease our dream recall. If you want to influence what you dream about, write down a question or goal for your dream in a dream journal—just before you go to bed. You will usually dream about your question or goal within a week."
As for the green snakes invading your body, that would seem to be an apt metaphor for the medication working their way into and through your body. Here are links to the relevant symbol definitions that support it...
snake:
dreamdoctor.com/dream-dictionary/definitions/snake.html
worm:
dreamdoctor.com/dream-dictionary/definitions/worm.html
Hope that helps!
