Nicotine, the main active ingredient in cigarettes, is a stimulant, a drug which increases brain activity. Found naturally in tobacco plants, this chemical is responsible for increased awareness and addiction which catapulted smoking to its spot among the most popular of vices. However, nicotine causes harmful side effects above a certain dosage – if left untreated, nicotine poisoning can result in seizures, comas, and even death. Although smoking rarely causes nicotine poisoning, consuming nicotine by mouth is much more likely to accumulate toxic levels of nicotine. 

To understand more about the dangers surrounding nicotine-containing plants, this article investigates the toxicity and uses of plants containing nicotine. It then looks at the symptoms, treatment and prevention of nicotine poisoning resulting from the ingestion of these plants.

How does nicotine affect the brain?

To understand nicotine’s effects on the brain, one must first understand how the brain works. The brain contains many neurones, nerve cells which act as wires to transmit electrical impulses for brain signalling. Neurones communicate with each other by releasing neurotransmitters at the gap between two neighbouring neurones (synapse). The neurotransmitter diffuses from the presynaptic neurone across the synapse, finally binding to receptors on the surface of the postsynaptic neurone. Depending on the neurotransmitter and corresponding receptor, the neurone’s charge changes, causing signalling intensity to either increase or decrease. 

Nicotine affects the receptors known as nicotinic acetylcholine receptors (nAChR), which are usually activated by binding of the neurotransmitter acetylcholine. After nicotine enters the bloodstream, it is transported across the blood-brain barrier into the brain. It then binds to nAChR, activating the receptor even in the absence of acetylcholine. A pore in the receptor opens, allowing positive ions (or cations) to enter the neurone. The neurone is depolarised – it becomes positively charged, leading to an increase in signalling – also known as excitation.¹ 

Toxicity of nicotine

The toxicity of nicotine is commonly cited to be 30-60 mg in adults, but some studies suggest the actual lethal dosage is much higher.² Excitation causes an uptick in brain activity, including an increased release of dopamine, causing the addictive feeling that nicotine is known for. 

In small amounts, nicotine causes arousal, reduces stress and anxiety, and enhances learning and sensory performance. However, high nicotine dosages leads to overexcitation – a condition in which there is too much activity in the brain. This results in nicotine poisoning. 

Which plants contain nicotine?

Nicotine can be found in plants from the Solanaceae family, commonly known as the nightshades. The Solanaceae are rich in a type of psychoactive (able to affect brain function) chemicals called alkaloids, of which nicotine is a prominent representative. Aside from the infamous tobacco plants, from which cigars and cigarettes are made, tomatoes, potatoes, aubergines, and peppers are all nightshades that we frequently find in our diet.

These plants contain only trace amounts of nicotine (2−7 μg/kg) compared to tobacco plants (3-7 g/kg).^3,4 Such small quantities of nicotine are unable to cause the increased awareness and relaxation characteristic of nicotine, let alone induce toxic effects. Don’t worry about eating your favourite fruits and vegetables!

Uses of tobacco plants

Native to South America, tobacco plants have played a significant role in many cultures throughout human history. Chewing and smoking of tobacco leaves are common in many native American cultures for religious, medicinal and recreational purposes. Tobacco was introduced to Europe around the 16^th century, and later exported to Africa and Asia. 

Although the adverse effects of tobacco have been observed by scholars as early as the 17^th century, it wasn’t until the 20^th century that widespread campaigns against smoking tobacco took place. Tobacco companies were no longer allowed to advertise their products to the public, and warnings detailing the harmful effects of tobacco must be printed on the package of tobacco products. 

Nowadays, alternative products such as vapes and nicotine replacement therapies (including nicotine patches and gums) are suggested to help people quit smoking. Although these products still contain nicotine, they lack other toxic chemicals found in tobacco smoke, making them preferable alternatives.

Nicotine has also been used as a pesticide in agriculture due to its toxic effects on insects, either in the form of tobacco extracts or pure nicotine sulfate. However, it is now banned in many countries – due to health concerns, and indiscriminate harm to all insects including pollinators (e.g. bees).¹ 

Tobacco ingestion

Compared to smoking and chewing tobacco leaves, consumption of tobacco by mouth is more likely to accumulate toxic doses of nicotine in the body. Using cigarettes as an example, an average cigarette contains 10-12 mg of nicotine. Most of this nicotine is burned when smoking, leaving only 1-2 mg to be inhaled into the body. In contrast, swallowing a cigarette will ingest all 10-12 mg of nicotine into the body.

Historically, most cases of accidental nicotine ingestion were due to the use of nicotine as an insecticide in agriculture. This has decreased in recent years after the ban of this practice. Workers in tobacco farms are also more likely to get tobacco poisoning from handling green tobacco (i.e. wet tobacco leaves), as the moisture allows nicotine to enter the body through skin contact. Tobacco can be ingested either by accident – such as the accidental swallowing of a cigarette, or on purpose – as a method of suicide.¹  

Infants are more susceptible to nicotine poisoning, both due to their natural inclination to put everything in their mouths and because less nicotine is needed to cause toxicity. While this can occur when a young child unwittingly swallows a cigarette, it is more often the result of drinking the liquid nicotine contained in vapes. 

Symptoms of nicotine poisoning

Nicotine poisoning occurs in two phases. Symptoms can begin a few minutes after nicotine ingestion – known as the first phase. If left untreated at higher doses (>0.5 mg/kg body weight), the second phase can occur. The first phase takes place less than one hour after initial nicotine ingestion, while the second phase occurs one to four hours after nicotine ingestion.

Symptoms of the first phase include:

• Nausea and vomiting
• Abdominal pain
• Feelings of restlessness or confusion
• Muscle twitching and tremors
• Loss of balance and decreased control over body movements (ataxia) 
• Increased heart rate and blood pressure
• Faster and heavier breathing (hyperpnea)

Symptoms of the second phase include:

• Seizures
• Slower and shallower breathing (respiratory depression)
• Sudden stop in heart beat (cardiac arrest)
• Fainting or coma
• Death

Prevention and treatment

The easiest method to prevent nicotine poisoning is to prevent the ingestion of tobacco products and other products containing nicotine. Store tobacco products out of the reach of children and educate on why it is important to prevent children's access to tobacco products. If tobacco leaves are ingested, get immediate medical help. Do not induce vomiting unless told to do so by healthcare professionals. 

Nicotine poisoning can be diagnosed by blood or urine tests, which can detect the levels of nicotine and/or nicotine metabolites (chemicals resulting from the breakdown of nicotine) in the body. Symptoms of nicotine poisoning can be treated by various medications. 

Activated charcoal can be ingested to absorb nicotine from the gut. Benzodiazepine, a depressant, has an opposite effect from nicotine in that it reduces brain activity. Administration of this drug can help control seizures. Atropine is used to treat decreased heart beat by blocking the electric impulses which signal for a slower heart rate. Ventilators can also be used to deliver oxygen in the case of respiratory depression. If a person survives the first four hours of nicotine poisoning (the second phase), they are likely to make a full recovery. 

Summary

Nicotine increases brain activity, which may lead to unpleasant or dangerous symptoms in high dosages. Found naturally in tobacco plants, it has played a considerable role in many cultures throughout history. Ingesting tobacco leaves is more likely to cause nicotine poisoning than traditional methods of using tobacco, such as smoking and chewing tobacco leaves. This is because ingesting tobacco allows the body to absorb more nicotine, making it more likely for nicotine to accumulate to toxic levels.

Symptoms of nicotine poisoning can be separated into a first phase with lighter symptoms, and a second phase with more dangerous symptoms. If tobacco is ingested or symptoms of nicotine poisoning occur, get immediate medical help. Different medications can be used to treat nicotine poisoning, and the patient is likely to recover if they survive the first, and most dangerous, four hours after initial ingestion.