Cannabis: What Science Says

A review of what the current scientific consensus is on the risks and benefits of cannabis use.

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The History of Cannabis

The use of cannabis dates back to at least the third millennium BC. It was used by the ancient Egyptians, Greeks, and Romans for its psychoactive properties. The plant was also used medicinally in China and India. In the 20th century, it was made illegal in many countries.

Early Use

Cannabis has been used for centuries for its medicinal and psychoactive effects. The first recorded use of cannabis dates back to 2737 BC, when it was used by Chinese Emperor Shen Neng as a treatment for gout, malaria and rheumatism.

In ancient Greece and Rome, cannabis was used as a topical treatment for pain and inflammation. In the Middle Ages, it was used as an anaesthetic during surgery.

In the 18th and 19th centuries, cannabis was widely used as a medical treatment for a variety of conditions, including migraines, seizures, muscle spasms and anxiety. It was also used to treat chronic pain and increase appetite in people with wasting diseases such as cancer and AIDS.

The first laws restricting the use of cannabis were passed in the early 20th century. In the United States, the federal government criminalized cannabis in 1937 with the Marijuana Tax Act. In Canada, cannabis was prohibited in 1923 under the Opium and Drug Act.

Modern Use

Cannabis use first appeared in the written record over 5,000 years ago in Taiwan. It then spread throughout ancient China and eventually made its way to India, Nepal, Tibet, and Central Asia. By the first century A.D., it had reached ancient Persia (modern-day Iran) and was being used medicinally by both the Chinese and Persians.

The earliest record of cannabis in the West comes from the Greek historian Herodotus (ca. 480–425 B.C.), who wrote of the Scythians—a group of Iranian people who were experts inhorsemanship—using cannabis to get high: “When they have a mind to feast with dry cinders covered with hemp seed [cannabis], they arrange rows of sticks upon which they throw some of these seeds, and then applying a sort of torch to the whole, they walk away to take their seats elsewhere at some little distance, so as not be affected by fumes; while their companions after lighting up the seeds smeared over with resin[another type of drug], placed on small pieces of charcoal, throw them into iron pans containing a little water, which are then covered so as not to let any steam escape . . . The company present then take some of the water that is under the pan into which they have thrown the seeds, and drink it off just as it is; another person takes hold of some thin plates of iron [hot coals], throws on them a handful of hemp seed , and puts them under his cloak . . .”

The Scythians were not alone in using cannabis for traditional ceremonies or medicinal purposes. The ancient Celtics also used it for religious rituals. In fact, one Celtic legend has it that when Hercules was traveling through Gaul (present-day France), he slept in a field of hemp plants and dreamt that he had been instructed by Apollo—the god of prophecy—to adopt this new plant as his own sacred emblem.

The Science of Cannabis

Cannabis is a plant that has been used for centuries for various purposes, including medicine, recreation, and fiber. The plant contains hundreds of chemicals, including over 60 compounds that are unique to the plant genus Cannabis. These chemicals are called cannabinoids.


Cannabis contains more than 100 different chemical compounds known as cannabinoids. Two of the main ones are THC and CBD.

THC is the main psychoactive compound in cannabis. It’s what makes you feel “high.” THC can be used for medical purposes, but it can also have certain side effects, including:

-impaired memory
-reduced ability to focus
-increased heart rate

CBD is another main compound in cannabis. It does not have the same psychoactive effects as THC, but it does have some potential medical benefits, including:
-reducing inflammation
-pain relief
-anxiety relief
-nausea reduction

The Endocannabinoid System

The endocannabinoid system (ECS) is a group of cannabinoid receptors located in the brain and throughout the central and peripheral nervous systems, consisting of neuromodulatory lipids and their receptors. The endocannabinoid system is involved in a variety of physiological processes including appetite, pain-sensation, nausea, mood, memory, metabolism, immune function, reproduction, stress relief, anxiety relief, and seizure prevention. The ECS is also involved in mediating some of the psychoactive effects of cannabis.

The Health Benefits of Cannabis

Cannabis has been shown to have a variety of health benefits, including reducing inflammation, pain relief, and more.

Pain Relief

One of the most well-known and well-studied effects of cannabis is pain relief. Cannabis’s pain-relieving properties are thought to come from its ability to interact with receptors in the brain and nervous system. These receptors are part of the body’s endocannabinoid system, which helps regulate pain, mood, and memory.

Studies have shown that cannabis can be effective in treating a variety of types of pain, including:
-Chronic pain
-Pain caused by inflammation
-Nerve pain
-Pain from cancer and cancer treatments
-Muscle pain

Cannabis is thought to be particularly effective in treating chronic pain, or pain that lasts for more than three months. This is the kind of pain that can be difficult to treat with other medication. Cannabis is also thought to be effective in treating inflammation-related pain, such as that caused by arthritis.

Anxiety and Depression

Cannabis has been shown to be effective in treating anxiety and depression. In one Brazilian study, 57% of patients reported that cannabis decreased their anxiety levels, while 43% said it increased their ability to engage in activities they enjoyed.

A small study of 24 patients with social anxiety disorder found that those who took a single dose of CBD (600 mg) before speaking in public reported significantly less anxiety and discomfort compared to those who took a placebo.

In a large survey of 2,013 US adults, 22% of respondents reported using cannabis in the past year for reasons including anxiety, depression, and stress relief. Of those people, 79% said it was “extremely or very effective” in relieving their symptoms.


Cannabis has been shown to kill cancer cells in laboratory studies. It has also been shown to reduce the spread of cancer and slow the growth of tumors. In animal studies, cannabinoids have been shown to reduce the size of tumors and increase the life expectancy of animals with cancer. Cannabis is not a cure for cancer, but it can be used as part of a treatment plan.

The Risks of Cannabis

Cannabis, also known as marijuana, is a popular drug that is used recreationally by people all over the world. While many people believe that cannabis is harmless, the reality is that it can actually be quite harmful. Cannabis has been linked to a number of health risks, including: mental health problems, addiction, impaired cognitive function, and respiratory problems.

Short-Term Effects

Short-Term effects of cannabis
Cannabis affects people differently, depending on factors such as their size, weight and health, how frequently they use it, the strength of the cannabis, and whether they smoke it or consume it in food or other forms. Short term effects of using cannabis can include:
-impaired ability to: remember, concentrate, pay attention, react quickly
-altered sense of time and space
-impaired body movement
-decreased blood pressure, which can cause people to faint
-increased heart rate, which can be dangerous for people with heart conditions and can lead to an increased risk of heart attack
-anxiety and paranoia

Long-Term Effects

Though more research is needed, it’s thought that the chronic (long-term) effects of smoking cannabis are similar to the effects of smoking tobacco. These effects might include risks to lung health, such as:

-Coughing and increased mucus buildup in the chest;
-Increased risk of lung infections;
-Obstructed air flow in the lungs; and
-Lung inflammation.

Chronic (long-term) use of cannabis might also lead to:

-Decreases in IQ;
-Anxiety and depression;
-Problems with memory and attention;
-Decreased motivation; and
-Psychosis (a break from reality).

The Future of Cannabis


The legal status of cannabis has been a long-standing and controversial topic. As more countries around the world move towards legalization, the debate is heating up. So, what does the future hold for cannabis?

It is difficult to predict the exact future of cannabis, but it seems likely that the trend is moving towards greater legalization. In the past few years, we have seen a number of countries decriminalize or legalize cannabis for recreational use. Canada became the second country in the world to legalize recreational cannabis in 2018, and a number of US states have also made progress on this front. Uruguay became the first country to fully legalize cannabis in 2013.

The legal landscape is changing rapidly and it is hard to say where things will stand in 5 or 10 years. However, it seems likely that more and more countries will move towards some form of legalization. This could mean good news for the global cannabis industry, which is expected to grow substantially in the next few years.

Medical Research

Research on the medical use of cannabis (marijuana) is ongoing. Much of the research to date has focused on the potential for cannabis as a treatment for certain medical conditions, especially pain relief, control of nausea and vomiting, and appetite stimulation.

Cannabis has been shown to be effective in reducing pain in various studies, including a 2010 study showing that cannabis can reduce nerve pain in people with HIV/AIDS. A 2012 study found that cannabis could be helpful in treating inflammatory bowel diseases like Crohn’s disease. And a 2016 review of studies concluded that cannabinoids (the active compounds found in cannabis) could be helpful in treating cancer-related side effects like pain and nausea.

There is also some evidence that cannabis can help improve sleep quality for people with certain medical conditions like chronic pain and multiple sclerosis.

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