Precisely, yes.
If I were to tell you that last year in India my wife and I both took Malarone for malarial prophylaxis and for the period of a week had trouble sleeping and anxiety—which happened, by the way—someone might tell us...but at the same time, her mother had a respiratory infection and was in an intensive care unit in India. Perhaps that would account for our trouble sleeping.
Would you not agree that to say you took this drug and had these symptoms, you need to control for all other variables?