Alcohol damages the brain more than cannabis, new research suggests.
Unlike booze, marijuana does not affect the size or integrity of white or grey matter in the brain, even after years of exposure, a study found.
Grey matter enables the brain to function, while white controls communication between nerve clusters.
Study author Professor Kent Hutchison from the University of Colorado Boulder, said: "While marijuana may also have some negative consequences, it definitely is nowhere near the negative consequences of alcohol."
The scientists add, however, research into cannabis' mental effects are still very limited.
Lead author Rachel Thayer said: "Particularly with marijuana use, there is still so much that we don't know about how it impacts the brain."
In the US, 44 percent of those aged 12 or over have used cannabis at some point in their lives.
Despite their findings, the researchers add there are still many holes in marijuana's safety.
Professor Hutchison said: "When you look at the research much more closely, you see that a lot of it is probably not accurate. When you look at these studies going back years, you see that one study will report that marijuana use is related to a reduction in the volume of the hippocampus [a region of the brain associated with memory and emotions]. 'The next study then comes around, and they say that marijuana use is related to changes in the cerebellum or the whatever. The point is that there's no consistency across all of these studies in terms of the actual brain structures. We still have a lot of work to do."
Although their findings appear positive, the researchers also add there is a long way to go before cannabis will likely be broadly legalized. Many are still concerned as to how the drug affects people of different ages, manages pain and causes addiction.
Professor Hutchison said: "Considering how much is happening in the real world with the legalization movement, we still have a lot of work to do."
The researchers analysed 853 adults aged between 18 and 55, as well as 439 teenagers aged 14-to-18 years old.
The study's participants' alcohol and cannabis use over the past 30 days was investigated.
MRI scans were taken of the participants' brains.
This comes after research released last month found a drug derived from cannabis reduces certain epilepsy patients' risk of a fit by nearly 50 percent.Sufferers of Lennox-Gastaut syndrome, which is a rare, severe form of the condition, are 43.9 percent less likely to have a drop seizure if they take the medication every day for 14 weeks, a US study found.
Drop seizures cause a brief lapse of muscle tone and usually last less than 15 seconds.Christina SanInocencio, executive director of the Lennox-Gastaut Syndrome Foundation, said: "Additional treatment options are desperately needed for patients who continue to struggle with uncontrolled seizures and these results offer much needed hope to those living with this debilitating condition."
The drug, known as Epidiolex, contains cannabidiol, which is a cannabis-derived nutritional supplement that is thought to possess a range of medicinal benefits and has been reported to help people suffering from migraines, psoriasis, acne and depression.