Memory and learning
Research shows that regular marijuana use compromises the ability to learn and to remember information by impairing the ability to focus, sustain, and shift attention. One study also found that long-term use reduces the ability to organize and integrate complex information.
In addition, marijuana impairs short-term memory and decreases motivation to accomplish tasks, even after the high is over. In one study, even small doses impaired the ability to recall words from a list seen 20 minutes earlier.
Marijuana use is associated with increased prevalence of depression, schizophrenia and psychosis. It remains unclear whether marijuana triggers the onset of these illnesses only in vulnerable people or whether it can cause them in people who would not have developed them otherwise.
Long-term marijuana use suppresses the production of hormones that help regulate the reproductive system. For men, this can cause decreased sperm counts and sperm motility and heavy users can experience erectile dysfunction. Women may experience irregular periods from heavy marijuana use. These problems would most likely result in a decreased ability to conceive but not lead to complete infertility.