Marijuana

A recent review of studies on marijuana tried to come to conclusions about its medical value. This is difficult because studies have multiple motives and marijuana is not one chemical but rather a combination of its cannabinoids and chemicals, which number in the hundreds, all working together to make its effects as potent as possible. So pinpointing the active ingredients is very hard. And good studies are difficult when doing evaluations of subjective parameters.
One major caveat to this: The report is, by its own admission, only a best guess for a lot of its findings, because much of the research out there just isn’t very good. By combing through more than 10,000 studies published since 1999, the review, conducted by more than a dozen experts, provides the clearest look at the scientific evidence on marijuana yet.
Remember: consensus of bad studies are worthless.


There is “conclusive evidence” that marijuana is good for treating chronic pain.
The report also found “conclusive evidence” that marijuana is effective for treating chemotherapy-induced nausea and vomiting.
And the report found “conclusive evidence” that marijuana can improve patient-reported multiple sclerosis spasticity symptoms. But it only found “limited evidence” for marijuana improving doctor-reported symptoms of this kind.
The report found “moderate evidence” that marijuana is effective for “improving short-term sleep outcomes in individuals with sleep disturbance associated with obstructive sleep apnea syndrome, fibromyalgia, chronic pain, and multiple sclerosis.” It also found “limited evidence” for marijuana’s ability to treat appetite and weight loss associated with HIV/AIDS, improving Tourette syndrome symptoms, improving anxiety symptoms in individuals with social anxiety disorders, and improving PTSD. And there’s “limited evidence” of a correlation between marijuana and better outcomes after a traumatic brain injury.
There is “limited evidence” that marijuana is ineffective for treating symptoms associated with dementia and glaucoma, as well as depressive symptoms in individuals with chronic pain or multiple sclerosis. And it found “no or insufficient evidence” for marijuana as a treatment for cancers, cancer-associated anorexia, irritable bowel syndrome, epilepsy, spasticity in patients with paralysis due to spinal cord injury, amyotrophic lateral sclerosis, Huntington’s disease, Parkinson’s disease, dystonia, drug addiction, and schizophrenia. 
Overall, the report suggests that, as far as therapeutic benefits go, marijuana is a solid treatment for multiple symptoms associated to chronic pain, chemotherapy-induced nausea and vomiting, and multiple sclerosis. 

The report finds “substantial evidence” of marijuana’s negative effects for a few conditions. For long-term marijuana smokers, there’s a risk of worse respiratory symptoms and more frequent chronic bronchitis episodes. For pregnant women who smoke pot, there’s a risk of lower birth weight for the baby. For marijuana users in general, there’s a greater risk of developing schizophrenia and other psychoses. And there’s a link between marijuana use and increased risk of car crashes.

The report also found “limited evidence” of links between marijuana use and several other negative outcomes, including an increased risk of testicular cancer, triggering a heart attack, chronic obstructive pulmonary disease, and pregnancy complications. And it found “moderate” to “limited” evidence that marijuana use might worsen symptoms or risk for some mental health issues, including depressive disorders, bipolar disorder, suicidal ideation and suicide attempts among heavier users, and anxiety disorders, particularly social anxiety disorder among regular users.

There’s “moderate evidence” that acute marijuana use impairs learning, memory, and attention. There’s “limited evidence” of marijuana use and worse outcomes in education, employment, income, and social functioning. There was some good news: The report found “moderate evidence” of no link between marijuana smoking and lung cancer or marijuana use and head and neck cancers, which are commonly linked to tobacco.

It also found a “limited” to “moderate” evidence of a correlation between marijuana use and use of other illicit drugs. This is the typical evidence cited for the so-called “gateway” effect: that marijuana use may lead to the use of harder drugs.