Several studies link alcohol with violence, particularly at home. That has not been found for cannabis.
It's impossible to say whether drinking alcohol or using marijuana causes violence, but several studies suggest a link between alcohol and violent behavior.
According to the National Council on Alcoholism and Drug Dependence, alcohol is a factor in 40% of all violent crimes, and a study of college students found that the rates of mental and physical abuse were higher on days when couples drank.
On the other hand, no such relationship appears to exist for cannabis. A recent study looking at cannabis use and intimate partner violence in the first decade of marriage found that marijuana users were significantly less likely to commit violence against a partner than those who did not use the drug.
Both drugs negatively affect your memory — but in different ways. These effects are the most common in heavy, frequent, or binge users.
Both weed and alcohol temporarily impair memory, and alcohol can cause blackouts by rendering the brain incapable of forming memories. The most severe long-term effects are seen in heavy, chronic, or binge users who begin using in their teens.
Studies have found that these effects can persist for several weeks after stopping marijuana use. There may also be a link between daily weed use and poorer verbal memory in adults who start smoking at a young age.
Chronic drinkers display reductions in memory, attention, and planning, as well as impaired emotional processes and social cognition — and these can persist even after years of abstinence.
Both drugs are linked with an increased risk of psychiatric disease. For weed users, psychosis and schizophrenia are the main concern; with booze, it's depression and anxiety.
The largest review of marijuana studies found substantial evidence of an increased risk among frequent marijuana users of developing schizophrenia — something that studies have shown is a particular concern for people already at risk.
Weed can also trigger temporary feelings of paranoia and hostility, but it's not yet clear whether those symptoms are linked with an increased risk of long-term psychosis.
On the other hand, self-harm and suicide are much more common among people who binge drink or drink frequently. But scientists have had a hard time deciphering whether excessive alcohol use causes depression and anxiety or whether people with depression and anxiety drink in an attempt to relieve those symptoms.