Regularly smoking cannabis may damage users’ eyesight by triggering an abnormality in the retina, a new study has found.
Researchers in France tested 28 cannabis smokers and 24 people who did not use the drug to see how well their retinal cells responded to electrical signals.
A small but significant delay was found in the time taken for the signals to be processed by the retina of the marijuana users by comparison with the control group.
“This finding provides evidence for a delay of approximately 10 milliseconds in the transmission of action potentials evoked by the retinal ganglion cells,” the researchers wrote in the JAMA Ophthalmology.
“As this signal is transmitted along the visual pathway … to the visual cortex, this anomaly might account for altered vision in regular cannabis users.
“Our findings may be important from a public health perspective since they could highlight the neurotoxic effects of cannabis use on the central nervous system as a result of how it affects retinal processing.”
A statement issued by the Journal of the American Medical Association described the study as “small” and “preliminary”.
But the researchers, led by Dr Vincent Laprevote, of the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy, added: “Independent of debates about its legalisation, it is necessary to gain more knowledge about the different effects of cannabis so that the public can be informed.
“Future studies may shed light on the potential consequences of these retinal dysfunctions for visual cortical processing and whether these dysfunctions are permanent or disappear after cannabis withdrawal.”
In a related article commenting on the research, Dr Christopher Lyons, of the University of British Columbia in Vancouver, and Dr Anthony Robson, of Moorfields Eye Hospital, London, wrote that it dealt with “an important and neglected issue, namely the possible toxic effects of cannabis, with all its implications for the many users of this ubiquitous drug”.
“Addressing this issue through the visual system, as the authors have done, is an elegant concept. Any deleterious effect on the visual system would also have implications for driving, work and other activities and thus warrants further study,” they added.
World's 10 most deadly street drugs
World's 10 most deadly street drugs
1/10 10. Purple Drank
One of the more unusual drugs around at the moment, purple drank was popularised in 90s hip hop culture, with the likes of Jay Z and Big Moe all mentioning it in their songs. It is a concoction of soda water, sweets and cold medicine, and is drunk due to cold medicines high codeine content, which gives the user a woozy feeling. However it can also cause respiratory issues and heart failure
2/10 9. Scopolamine
Scopolamine is a derivative from the nightshade plant found in the Northern Indian region of South America (Ecuador, Colombia and Venezuela). It is generally found in a refined powder form, but can also be found as a tea. The drug is more often used by criminals due its high toxicity level (one gram is believed to be able to kill up to 20 people) making it a strong poison. However, it is also believed that the drug is blown into the faces of unexpecting victims, later causing them to lose all sense of self-control and becoming incapable of forming memories during the time they are under the influence of the drug. This tactic has reportedly been used by gangs in Colombia where there have been reports of people using scopolamine as way to convince victims to rob their own homes
3/10 8. Heroin
Founded in 1874 by C. R. Alder Wright, heroin is one of the world’s oldest drugs. Originally it was prescribed as a strong painkiller used to treat chronic pain and physical trauma. However in 1971 it was made illegal under the Misuse of Drugs Act. Since then it has become one of the most destructive substances in the world, tearing apart communities and destroying families. The side effects of heroin include inflammation of the gums, cold sweats, a weak immune system, muscular weakness and insomnia. It can also damage blood vessels which can later cause gangrene if left untreated
4/10 7. Crack cocaine
Crack cocaine first came about in the 1980’s when cocaine became a widespread commodity within the drug trafficking world. Originally cocaine would have attracted a high price tag due to its rarity and difficulty to produce, but once it became more widespread the price dropped significantly. This resulted in drug dealers forming their cocaine into rock like shapes by using baking soda as a way of distilling the powder down into rock form. People were doing this because it allowed for them to sell cocaine at a lower quantity and to a higher number of people. The side effects of crack cocaine include liver, kidney and lung damage, as well as permanent damage to blood vessels, which can often lead to heart attacks, strokes, and ultimately death
5/10 6. Crystal meth
Not just famous because of a certain Walter H White, but also because it is one of the most destructive drugs in the world. First developed in 1887, it became widely used during the Second World War when both sides would give it to their troops to keep them awake. It is also believed that the Japanese gave it to their Kamikaze pilots before their suicide missions. After the war crystal meth was prescribed as a diet aid and remained legal until the 1970s. Since then it has fallen into the hands of Mexican gangs and has become a worldwide phenomenon, spreading throughout Europe and Asia. The effects of crystal meth are devastating. In the short-term users will become sleep depraved and anxious, and in the long-term it will cause their flesh to sink, as well as brain damage and damage of the blood vessels
6/10 5. AH-7921
AH-7921 is a synthetic opioid that was previously available to legally purchase online from vendors until it became a Class A in January 2015. The drug is believed to have 80% of the potency of morphine, and became known as the ‘legal heroin’. While there has only been one death related to AH-7921 in the UK, it is believed to be highly dangerous and capable of causing respiratory arrest and gangrene
7/10 4. Flakka
Flakka is a stimulant with a similar chemical make-up to the amphetamine-like drug found in bath salts. While the drug was originally marketed as a legal high alternative to ecstasy, the effects are significantly different. The user will feel an elevated heart rate, enhanced emotions, and, if enough is digested, strong hallucinations. The drug can cause permanent psychological damage due to it affecting the mood regulating neurons that keep the mind’s serotonin and dopamine in check, as well as possibly causing heart failure
8/10 3. Bath salts
Bath salts are a synthetic crystalline drug that is prevalent in the US. While they may sound harmless, they certainly aren’t the sort of salts you drop into a warm bath when having a relaxing night in, they are most similar to mephedrone, and have recently been featured throughout social media due to the ‘zombification’ of its. The name comes from the fact that the drug was originally sold online, and widely disguised as bath salts. The side effects include unusual psychiatric behaviour, psychosis, panic attacks and violent behaviour, as well as the possibility of a heart attack and an elevated body temperature
9/10 2. Whoonga
Whoonga is a combination of antiretroviral drugs, used to treat HIV, and various cutting agents such as detergents and poisons. The drug is widely available in South Africa due to South Africa’s high rate of HIV sufferers, and is believed to be popular due to how cheap it is when compared to prescribed antiretrovirals. The drug is highly addictive and can cause major health issues such as internal bleeding, stomach ulcers and ultimately death
10/10 1. Krokodil
Krokodil is Russia’s secret addiction. It is believed that over one million Russians are addicted to the drug. Users of krokodil are attracted to the drug due to its low price; it is sold at £20 a gram while heroin is sold for £60. However, krokodil is considered more dangerous than heroin because it is often homemade, with ingredients including painkillers, iodine, lighter fluid and industrial cleaning agents. This chemical make-up makes the drug highly dangerous and likely to cause gangrene, and eventually rotting of the flesh
"Electrophysiology can provide reliable and reproducible measurements of retinal and visual pathway function and is useful in the investigation and localisation of dysfunction, including that caused by toxicity.
“However, the conclusion that cannabis causes retinal ganglion cell dysfunction cannot be made with any degree of certainty based on the evidence provided in the current study.
“This question should be re-examined with some urgency, using a degree of scientific rigour, which may be challenging in jurisdictions where cannabis consumption is illegal.”