Most alkaloids taste bitter to humans, and because bitter taste is synonymous of noxious food, they are generally rejected. This response may be due to an innate low palatability or due to a malaise that occurs after food ingestion, which could even lead to death.

Many plants contain toxic alkaloids which may be dangerous to humans. This review describes the toxic alkaloids aconitine, atropine, coniine, colchicine, cytisine, dimethyltryptamine, harmine, harmaline, ibogaine, kawain, mescaline, scopolamine, and taxine, which are often involved in fatal and non-fatal poisonings.

Alkaloids have diverse physiological effects: antibacterial, antimitotic, anti-inflammatory, analgesic, local anesthetic, hypnotic, psychotropic, and antitumor activity and many others. Well-known alkaloids include morphine, strychnine, quinine, atropine, caffeine, ephedrine, and nicotine [1].

Pyrrolizidine alkaloid toxic effects are mainly due to their biotransformation into strong reactive pyrrole structures by oxidases from the mammalian liver. The reactive pyrroles act by alkylating nucleic acids and proteins (Cushnie et al. 2014).

There are 30 known pyrrolizidine alkaloids that are hepatotoxic, meaning they cause injury to the liver. Although animals innately know to give these toxic plants a wide berth while grazing, in extreme drought conditions animals have been known to ingest them as a source of minimal protein.

Like lectins found in beans and grains, alkaloids are toxic in high amounts. But simply cooking these foods can significantly reduce the concentration and reduce any real cause for concern.

Alkaloids can be toxic too (e.g. atropine, tubocurarine). Although alkaloids act on a diversity of metabolic systems in humans and other animals, they almost uniformly evoke a bitter taste. The boundary between alkaloids and other nitrogen-containing natural compounds is not clear-cut.

Nearly all of the alkaloids mentioned so far are poisonous in large amounts. Some alkaloids, however, are almost solely known as poisons. One of these is strychnine, derived from the small Hawaiian tree Strychnos nux-vomica. In severe poisoning, a loud sound can cause severe muscle spasms throughout the entire body.

Nearly all of the alkaloids mentioned so far are poisonous in large amounts. Some alkaloids, however, are almost solely known as poisons.

Caffeine is the most common purine alkaloid, but in a few plant species including cacao and unique Chinese tea plants, the main purine alkaloid is theobromine or methyluric acid (Ashihara and Crozier, 1999; Ashihara and Suzuki, 2004). A large amount of caffeine is found in coffee seeds (mainly in endosperms).

Alkaloids can be dangerous in large doses. In fact, there are many other plants in the nightshade family that are poisonous to humans (like, ahem, tobacco). Even though they contain low levels of alkaloids, edible nightshades might, to some people, seem guilty by association.

Addressing the difference in toxicity between the tested alkaloids, the indole alkaloid gramine was the most toxic (48 h EC50: 6.03 mg/L), and heliotrine, lupanine and lupinine the least toxic (48 h EC50: > 100 mg/L), while the remaining alkaloids had toxicities in between (Table 2).

The general symptoms of alkaloid poisoning include nausea, fatigue, a numbing or tingling sensation in the fingers, and a strong dislike for the leafy green that is currently being consumed.

This is a classic example of how a person can be exposed to alkaloid poisoning. You may have gathered from our example that it took a lot of kale smoothies to cause alkaloid poisoning. The cause of plant-based alkaloid poisoning is quite easy to remember: It is the excess eating of leafy greens.

The cause of plant-based alkaloid poisoning is quite easy to remember: It is the excess eating of leafy greens. The term, ‘excess’ may vary from one person to another, as there are many factors to consider, such as body size, height, age, etc. However, the basic principle remains.

Humans and animals can be exposed to toxic alkaloids either through inhalation, swallowing or by direct contact, therefore leads to the specific mechanism that involves receptors, transporters, enzymes and genetic materials at specific cells and tissues, hence may cause hepatotoxic effects and musculoskeletal deformities.