People who abuse ketamine a lot (more than 4 times a week) have been found to have impaired memory and increased depression when compared to people who don't abuse ketamine. Those who use ketamine less frequently (1-4 times per week)and those who had stopped taking ketamine showed no difference in the aforementioned parameters. This suggests that these problems with memory and mood do not affect infrequent users and might be reversible once ketamine use is stopped.