The documented use of plants is as old as the existence of human beings on earth [1], for both feeding and healing purposes ^[2][3][2,3]. As per the survey report published by the World Health Organization (WHO), it is estimated that about 80% of the population from developing countries depend on traditional medicine for primary health care ^[4][5][6][7][4,5,6,7].

Medicinal plants are composed of a plethora of secondary metabolites, such as alkaloids, phenolics, flavonoids, terpenoids and glycosides, which act to protect them from adverse situations ^{[8][9][10][11][12]}[8,9,10,11,12]. Most plant products are biologically and pharmacologically useful because of their therapeutic properties, while others are toxic to both humans and animals due to the presence of harmful by-products [1]. These plants are known as poisonous plants, because of their toxic nature, and are widely distributed around the world, being used by indigenous people for hunting, fishing and the treatment of different diseases ^[13][14][13,14].

The toxic nature of a plant species vary from species to species, and depends on several factors, including chemical, physical, biological and environmental (presence of chemical substances, its concentration, age of plant, used part, ripening state of its fruits, soil type, temperature, humidity, etc.) [15]. The poisoning may result either from contact, which may cause skin irritation; ingestion, which may result in internal toxicity; absorption; or inhalation through the respiratory tract [16]. Plant toxins can be divided into several groups, such as gastrointestinal toxins, cardiovascular toxins, convulsive toxins, anti-cholinergic toxins, nicotine and nicotine-like alkaloids, calcium oxalate crystals and cellular respiration toxins [17] (Figure 1).

Most poisonings cases are characterized by irritations of the gastrointestinal tract, such as vomiting, nausea or severe diarrhea, and others by dermatological discomfort, such as dermatitis (Figure 2). However, there are more severe cases of poisonings, in which the central nervous system or cardiorespiratory function can be affected, and death can even occur [18]. Plant toxins are closely related to human and animal health aspects [19], and some toxic compounds might even be applied as effective treatments for human diseases [20].

The toxicity of poisonous plants in some cases resides in whole plant, while in other cases in some parts of the plant, such as the shoot, leaves, flower, seeds, bark or even latex [21]. The continuous research and development in plant knowledge has promoted a marked increase in the awareness and usefulness of plants for medicinal purposes [22], as well as on their toxicological profiles ^[23][24][23,24].

Most individuals are not familiar with the toxicity of most plants found around them, an aspect that is potentially harmful if they establish a direct contact or even ingest them. In animals, most poisonous plants cause poisoning when they are accidently grazed by them [25]. Despite local elderly people passing the knowledge of poisonous plants from one generation to the next one, it is very important to provide general awareness regarding their toxicological profiles [26]. Thus, the best approach for minimizing accidental intoxication with poisonous plants is to make people aware of plants’ toxicity and their harmful effects on them and other animals. This information should be dispersed in general by the population, childhood educators and official entities that together can play a special role in this sense.

The Indian Himalayan region (IHR) homes a huge variety of plant species that have been used in several ways, i.e., emergency food/nutraceutical, medicinal, pharmaceutical purposes, etc. [27]. The IHR has a large diversity of plants and most of them are known for their medicinal properties, with some of them being known for their toxicity. Poisonous plants of the IHR produce a variety of toxins that have negative effects on human and animal health, ranging from mild allergies to serious medical complication and even death. In India, it is estimated that more than 50,000 people die from toxic exposure every year, which is the highest number in the world, and plants account for 1.7% of all toxic exposures [28], and are mostly used for robbery and suicidal purposes. Poisoning is the fourth most common cause of mortality in India [29]. Poisonous plants most often affect grazing livestock, which is a major concern for both farmers and veterinarians. Grazing is considered a common routine in livestock management, but it exposes animals to a variety of poisonous plants, especially when there is a lack of fodder availability [30]. Animals that are already experiencing nutritional stress are more vulnerable to plant toxicity. The Indian subcontinent has the biggest population of the livestock in the world, accounting for about 7% of its income [31]. Sometimes, the lack of knowledge and unawareness from inhabitants means that they use these plants for food, fodder and medicinal purposes, or are even subjected to accidental exposure, which is sometimes life-threating to both humans and animals. Poisonous plants are harmful for livestock and causes of economic loss to the livestock sector. Some of the major poisonous plants of the IHR are further described below (Table 1).

2.1. Abrus precatorius

Linn.

The seeds of Abrus precatorius (Indian licorice, Fabaceae) are highly toxic and contain some active compounds, such as abrine, abrasine, abraline, abrin, abricin, abrusgenicacid, etc. [32]. Abrin is more toxic than the other active compounds, which is a toxalbumin that inhibits protein synthesis and causes cell death [33]. Even consuming one of its seeds can be fatal for both children and adults. The lethal dose or (LD₅₀) of abrin toxin for human is 0.1–1 µg/kg body weight [34].

2.2. Aconitum ferox

Wall. Ex Ser.

 (Syn Aconitum Atrox 

Walp

)

Aconitum ferox (Indian aconite, Ranunculaceae), is an erect and perennial herb whose distribution ranges from temperate to alpine regions of India, Nepal, Bhutan and China ^[35][36][37][35,36,37]. It is a rhizomatous poisonous herb, but with great pseudaconitine, veratroylbikhaconine, medicinal properties when used after vigorous purification and in the right amounts. Bikhaconitine, veratroylpseudaconine, norditerpenoid alkaloids and quinolinones are some active compounds present in the whole plant ^[38][39][38,39]. The plant is used as poison for arrow heads [40]. The lethal dose of aconitine in human is 2 to 6 mg/kg body weight [41].

2.3. Aconitum hookeri

Stapf.

Aconitum hookeri (Hooker’s Monkshood, Ranunculaceae) extends its distribution from India, Nepal, Bhutan and China [37]. The whole plant is reported as poisonous, but its rhizomes are used as a medicine [42].

2.4. Aconitum lethale

Griff.

 (Syn Aconitum Balfourii 

Stapf.

)

Aconitum lethale (Balfour’s Monkshood, Ranunculaceae) is an erect glabrous herb, whose main distribution is in Himalayan region. Aconitine, pseudoaconitine [43], balfourine ^[44][45][44,45], norditerpenoid alkaloids [46] are some active compounds found in this species. The whole plant is reported as toxic for humans and other animals.

2.5. Aconitum napellus

Linn.

Aconitum napellus (Violet Monkshood, Ranunculaceae) is a biennial plant, with geminate tubers. Stems are usually simple, erect in the lower part, glabrous or hairy [47]. It is generally distributed in the Himalayan region of Nepal, India, China, and Pakistan [48]. The primary toxin of A. napellus is aconitine, which is distributed throughout the plant, but its concentration is highest in its roots and leaves [17].

2.6. Aconitum spicatum (Brühl)

Stapf.

Aconitum spicatum (Nepal Aconite, Ranunculaceae) is a shrub species, usually sparsely pubescent and simple [36]. The root tubers of this species contain some active compounds such as aconitine, mesaconitine, bikhaconitie, deoxyaconitine, hypaconitine, spicatine A and B [49]. A. spicatum is highly toxic and used as arrow poison in Nepal Himalaya [50].

2.7. Aquilegia pubiflora

3.7. Aquilegia pubiflora 

Wall. Ex Royle

Aquilegia pubiflora (Himalayan Columbine, Ranunculaceae) is another important herb widespread in the Himalayan region of India, Pakistan and Afghanistan [51]. Isovitexin, isoorientin, vitexin, chlorogenic acid, orientin, cumeric acid, sinapic acid, ferulic acid are some active compounds found in this species [52].

2.8. Aesculus indica (

Wall. Ex Camb.

) 

Hoof. f.

Aesculus indica (Indian horse-chestnut or Himalayan horse chestnut, Hippocastanaceae) is widely distributed in low-temperature regions of the world, and is commonly found in North Western Himalaya in the Indian context [53]. A. indica is large sized deciduous and perennial tree species that attains a height of up to 20 m. It is widely used in traditional medicine systems to treat many diseases. A. indica is poisonous to humans and other animals due to the presence of a saponin-class toxin called escin or aesculin ^[54][55][54,55]. After ingestion, aesculin enters the blood and destroys red blood cells. The young leaves and flowers of this plant species are more toxic than mature leaves. The bark and seeds also contain small amounts of aescin [55]. A. indica poisoning can cause fatigue, paralysis, coma, and even death. The lethal dose or LD₅₀ was observed to be 10.6 mg/g body weight for chicks with a single dose of the seed extract (A. indica) and 10.7 mg/g body weight with hamster. Administration of A. indica for 2 consecutive days showed 6.5 mg/g LD₅₀ [54].

2.9. Cannabis sativa

Linn.

Cannabis sativa (Hemp or bhang, Cannabaceae) is one of the most important industrial crops distributed at global level [56] for its psychoactive resins. The native distribution of the species is in Central Asia, Siberia, China and the Himalayas [56]. C. sativa contains more than 400 active compounds, but the major psychoactive toxic constituents are 9-tetrahydrocannabinol (THC) and cannabidiol (CBD) [27]. The lethal dose or LD₅₀ of THC is not determined in humans, but in cattle, it was observed to be 40 to 130 mg/kg body weight [57].