Why or why not?

A study was conducted to test whether marijuana use impacts your short-term memory. A simple random sample of college students that do NOT use marijuana was taken, and given a memory test in which they were shown items in a particular order then asked to recreate that ordering. A second simple random sample was taken of college students that use marijuana 4 - 7 days per week, and they were given the same memory test. A higher score on the memory test indicates better memory recall. M1 indicates the population mean memory recall score for non-users. M2 indicates the population mean memory recall score for marijuana users. The 95% confidence interval for the difference of means was found to be: -2.6