One of the most fascinating topics in plant biochemistry is that of alkaloids.  Not only does this include the role in the plant but also covers the effects that they have in animal physiology and human society.

Chemically this family of compounds is quite diverse but in broad terms all of them contain carbon, oxygen, hydrogen, and nitrogen.  They're insoluble in water but dissolve in non polar organic solvents (oily) such as ether or chloroform.  They can dissolve in water if the pH is alkaline, hence the name alkaloid. 

Their roles are typically as insecticidal compounds but can also target grazing animals.  They are however found in organisms besides plants such as fungi, bacteria, insects, and frogs.  For the purpose of this blog post we are only going to cover ones from plants. They can also be synthesized by fungi such as mushrooms in the Psilocybe genus.  Also animals such as poison dart frogs can consume alkaloids from plants and incorporate them into their bodies.


two deer

Keeping in mind that there are hundreds of of different alkaloids, we are only going to discuss a few of the more common and interesting ones.  If there is interest we can certainly write a followup blog post in the future discussing others. 



Perhaps the most interesting chemical name out there, it literally means "food of the gods" in ancient Greek.  Probably this name came about since the consumption of chocolate was reserved for royalty in ancient Mesoamerican cultures and they were considered to be gods. This bitter tasting alkaloid is present in the highest concentrations in the cocoa plant and is found in much lower concentrations in tea and the kola nut. 

In humans its effects are similar to that of caffeine but to a lesser degree.  These include vasodilation, cardio stimulation, and being a dietetic.  


raw cocoa bean
Raw cocoa beans

A particularly noteworthy fact on this alkaloid is its toxicity to dogs.  While eating large amounts of chocolate can induce negative effects in humans we can metabolize theobromine relatively quickly.  Dogs break it down very slowly and so are more susceptible to poisoning.  Mild toxicity can result in vomiting and diarrhea.  Severe toxicity can result in heart attacks and even death.  White and milk chocolate are not as dangerous to dogs because they have significantly less theobromine than dark or baking chocolate. However, it’s nevertheless inadvisable to give any chocolate to dogs because they can quickly develop a taste for it.



By far the most used alkaloid, it is consumed daily by billions of people worldwide usually in the form of coffee, tea, chocolate, or energy drinks.  It is found in a total of 60 different species besides the obvious ones like tea and coffee.


tea plantation
A tea plantation


While considered to be a mild stimulant, it is habit forming and may cause the drinker to lose sleep or have mild anxiety.

*Did you know?*

It is possible to overdose on caffeine.  The base unit in toxicology is LD50 based on how many milligrams per kilogram (mg per kg) of body weight is needed to produce a lethal dose.  For caffeine that is 150-200 mg per kg.  That means that a 70 kg (154 lb) person would require 12250 mg (12.25 grams) in order to reach fatal levels.  Assuming the average cup of coffee has 150 mg of caffeine, someone would have to drink around 80 cups in order to risk having a lethal overdose. 



Ephedrines synthetic sister molecule pseudoephedrine was made famous as a precursor for methamphetamine in the popular TV series "Breaking Bad".  On its own ephedrine it's a mild to moderately strong stimulant and is used as a bronchodilator (opening up the lungs) as well as to increase blood pressure, a weight loss supplement and as a treatment for motion sickness.  Mild side effects include insomnia and irritability, stronger side effects include heart attack and stroke.  

Botanically it is associate with the genus Ephedra, which are shrubs typically found in many arid regions of the world.  It has been consumed both as a traditional medicine and as a stimulant, usually in the form of a tea.



While completely legal, it is one of the most additive drugs on the planet and is linked to a host of health problems including lung cancer, leukemia, heart disease, and diabetes.  The effects of smoking are well known so there's no need to go into too much detail here.

Botanically this alkaloid is found throughout the nightshade family including tomatoes, eggplants, and potatoes but in trace amounts.  In higher quantities its really only found in tobacco species and a few other plants.  It also has strong insecticidal properties but since it has powerful effects on mammals its usage in present times is limited. 

woman making cigars



The first "illegal" alkaloid on our list, it's typically associated with cacti such as peyote and San Pedro cactus.  In an environment where water is scarce these slow growing plants evolved a mechanism in which they produce mescaline in order to deter large herbivores from eating them.

While it is used a recreational drug it also has been used for at least 5700 years as a sacrament in shamanistic religious rituals. It is a known psychedelic comparable to LSD or psilocybin with effects such as visual hallucinations, and a distorted sense of time.  Side effects include diarrhea and vomiting, fear and anxiety, increased heart rate and accidental injury.



Like many on this list cocaine has a long history use by humans.  This time coming from plants in the Coca genus, a shrub native to the Andes in South America.  From coca leaves traditionally used for altitude sickness, to over the counter 19th century remedies, to crack epidemics - its usage has been very widespread.  It likely functions as an insecticide by the plant, however it's not very well understood.  In humans it is a powerful stimulant and in the short term gives energy, euphoria, alertness and feelings of competence.  It is very habit forming and side effects include paranoid delusions, anorexia, heart attack and stroke. 


old coca wine advertisement poster


*Did you know?*

In an attempt to eradicate cocaine production, glyphosate (Roundup) has been widely sprayed by air on coca plantations.  A strain called boliviana negra has been shown to be resistant to glyphosate and now dominates production in South America.  It was initially suspected that it was made in the lab, like resistant strains of soya and canola but upon further investigation it's been shown that it is naturally resistant.  Likely a field was sprayed and the farmer noticed that one of the plants lived.  From there it spread by cuttings all over the Andes.  Now a plantation being sprayed with glyphosate is welcome since it will give free weed control to the farmer by killing competing plants but leaving the coca bushes unharmed. 



The opium poppy, Papaver somniferum, produces a number of different alkaloids, morphine being the most abundant and most powerful.  Morphine along with these other opioids has been used as a pain killer since ancient times in the form of opium.  It is very addictive and tolerance grows over time.

Many synthetic opioids start out with morphine as the precursor.  For example heroin is simply a modified morphine molecule. 



While found in a wide variety of nightshades (Solanaceae) it is most well know in Datura species as well as Belladonna and Hensbane.  While most intoxicating chemicals are categorized as stimulants, depressants or psychedelic, this one is in a different category which is deliriant.  This means that the user will go into a state where all control is lost, which can be very unpleasant. 


Brugmansia (or tree Datura) Flower
Brugmansia (or tree Datura) Flower


It causes the body to lose control of involuntary functions such as sweating, breathing and heart rate.  

While small doses are used to treat motion sickness and nausea, larger ones are dangerous and it's been used for nefarious purposes such as an experimental truth serum and muggings. 


*Did you know?*

Zombies are a mainstay of the horror genre and the lore can be traced back to Haiti.  People would be drugged with "zombie dust" and they would fall into a state of near death and presumed dead and then buried.  The perpetrator would then dig up the person during the night and use them as slaves, usually cutting sugar cane.  The active ingredient in zombie dust is the toxin of puffer fish.  However to keep the zombie slaves docile they would regularly be fed a concoction containing scopolamine.



A very toxic alkaloid found in many different plants but principally extracted from Strychnos nux-vomica, the strychnine tree, which is found in India and South East Asia.  The concentrations are the highest in the seeds and protect the plant against grazing animals who might consume them.

The lethal dose is very small, around 1.5 - 2 mg per kg for humans.  For this reason it has long been used as a rodenticide and by those carrying out murder through poison.  It is starting falling out of favour because of accidental poisonings and the fact that it's an agonizing way to die.  Symptoms include seizure and convulsions.  Fatalities are from the victim being unable to breath.