Uncertainty over the effects of cannabis means it is best to be prudent  The debate over the effects of cannabis is based largely upon conflicting evidence. For example, some argue it can cause psychosis while others argue it only has positive effects on the mind. The effect of any illegal drug is a very difficult area to study 1. Most drug users use more than one drug and researchers are often limited to studying those who admit themselves into clinics with a crisis – something of a skewed sample.  Given that Governments cannot accurately predict what the effects of legalizing cannabis would be, it is prudent to maintain illegality. What if, for example, a state decided to legalize cannabis, to only discover five years later that it has a dramatically more negative impact on human cognition than previously thought, or that it substantially increased the risks of psychosis?  1.Wolff, 2009,