As cannabis becomes more widely used around the world, scientists are paying closer attention to how it may affect mental health.
While some people use cannabis to relax or reduce stress, others may develop serious problems linked to frequent use.
One growing concern is cannabis use disorder, often called CUD, a condition where a person struggles to control their cannabis use even when it starts causing problems in daily life.
People with cannabis use disorder may continue using the drug despite issues with work, school, relationships, memory, motivation, or mental health.
Some may also experience cravings, withdrawal symptoms, or difficulty cutting back. Researchers have been studying for years whether cannabis use disorder is connected to depression, but until now the relationship has not been fully clear.
A major new study has now found strong evidence that cannabis use disorder and major depressive disorder are closely linked. The findings were published in the Journal of Psychiatric Research.
The research involved a large meta-analysis, which is a scientific method that combines results from many earlier studies to look for overall patterns. In this case, researchers analyzed 55 studies involving more than 3 million people from different parts of the world.
The scientists found that about 31 percent of people with cannabis use disorder also had major depressive disorder, often called MDD. Major depressive disorder is a serious mental health condition that goes beyond normal sadness.
It can involve persistent low mood, loss of interest in activities, hopelessness, tiredness, sleep problems, appetite changes, difficulty concentrating, and thoughts of self-harm or suicide.
The study also found the connection works in the opposite direction. Around 10 percent of people with depression also met the criteria for cannabis use disorder. This suggests the two conditions may influence each other in complex ways.
An international team of researchers carried out the study by searching major scientific databases for studies published in English and Portuguese through 2024. They used advanced statistical methods to combine findings from millions of people while adjusting for factors such as age, sex, and geographic location.
One important finding was that the relationship between depression and cannabis use disorder changes depending on where people are studied.
Among members of the general public, rates of cannabis addiction among people with depression were lower. However, in psychiatric clinics and mental health treatment settings, the overlap became much stronger.
The researchers found that more than 28 percent of patients receiving treatment for depression also had cannabis use disorder. This suggests that people with more severe mental health problems may be especially vulnerable to problematic cannabis use.
The study also showed that the relationship between depression and cannabis use disorder often continues across a person’s lifetime. Even when depression was not currently active, many people with cannabis use disorder had experienced depression earlier in life.
According to the findings, about 20 percent of people with cannabis use disorder were depressed at the time of the study, while around 35 percent had experienced depression at some point during their lives.
Researchers say the relationship between cannabis and depression is likely very complicated. Some people with depression may use cannabis to cope with emotional pain, stress, anxiety, or sleep problems. Over time, however, heavy cannabis use may worsen mood problems, increase emotional instability, or reduce motivation.
At the same time, people with cannabis use disorder may develop social, financial, or health problems that contribute to depression. Scientists are still working to understand exactly how the two conditions influence each other.
The study also highlighted a major challenge doctors face when diagnosing these conditions. Symptoms of cannabis withdrawal can closely resemble symptoms of depression. For example, people stopping cannabis use may experience irritability, anxiety, sleep disturbances, low mood, and emotional distress.
Because these symptoms overlap, it can sometimes be difficult for doctors to determine whether a person has a true depressive disorder, withdrawal symptoms from cannabis, or both conditions together.
The researchers also noted limitations in the study. Much of the available research came from North America, which means the findings may not fully represent populations in other countries with different cultures, healthcare systems, or cannabis laws.
Still, the researchers believe the evidence is strong enough to support more regular screening in healthcare settings.
They recommend that doctors treating patients for depression should ask about cannabis use, while healthcare providers working with people who have cannabis use disorder should also check for symptoms of depression.
The authors explained that early identification may help prevent both conditions from becoming worse. Treating one condition without addressing the other could make recovery more difficult.
The findings arrive at a time when cannabis use is increasing in many countries due to changing laws and social attitudes. Some people view cannabis as harmless, but experts say heavy or long-term use can affect mental health in vulnerable individuals.
After reviewing the findings carefully, the study appears highly important because it combines evidence from millions of people and provides one of the clearest pictures so far of the relationship between cannabis addiction and depression.
However, the study does not fully prove that cannabis directly causes depression or that depression directly causes cannabis addiction. The relationship is likely influenced by many biological, psychological, and social factors.
Even so, the strong overlap between the two conditions suggests that mental health professionals should pay close attention to both problems when treating patients.
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Source: Journal of Psychiatric Research.
