I can't speak on pharmocology but I am currently taking General Organic and Biological Chemistry along with three other classes. It requires a lot of studying and dedication. Mostly, the formulas, balancing equations, and not the concept itself that are challenging. I work full-time which makes it especially challenging. I would save organic chemistry for a full semester.
You might want a full semester of organic and go at a steady pace. I'm sure that there are people who think organic wasn't bad, but honestly, it sucks. A compressed summer organic class...no thank you.