Sometimes the only difference between a pill and a poison is the dose. An aspirin, for example, will relieve pain. But 200 aspirins will kill you. Some substances are extremely toxic, and therefore, are primarily known as a poison. Yet, even poisons, like those listed below, can have medicinal value, Chris Kilham, a medicine hunter who researches natural remedies all over the world, explains on Fox News channel.

Snake venom

Snake venom, collected from farmed reptiles, has been used to make antivenom for snake bites for decades. To produce antivenom, pure snake venom is diluted and then injected into mammals such as sheep, goats, rabbits and horses. After being injected, the animal undergoes an immune response, and scientists can collect the antibodies produced by the animal to make the antivenom.

But making drugs from snake venom is a relatively new idea. For example, the protein disintegron eristostatin, extracted from the venom of the Asian sand viper, has been shown to help people’s immune systems fight malignant melanoma. Previous studies have shown that disintegron eristostatin stops melanoma cells from colonizing in the liver and lungs of mice. 

Tetrodotoxin

 An extremely potent neurotoxin, tetrodotoxin (TTX), derived from the pufferfish, is one of the most concentrated poisons known to man. TTX blocks voltage-gated sodium channels (VGSCs), which play a critical role in neuronal function. The administration of TTX at doses below those that produce acute toxic reactions in normal nerves has been used in humans and animals under different pain conditions. 

Nightshade

Deadly Nightshade, or Atropa belladonna, has a long and rich history of use as a lethal poison. Over the centuries, Deadly Nightshade has been used for poisoning enemy troops in war, as an implement of torture, for its extreme hallucinogenic activity, and reportedly for witchcraft, applied as a vaginal ointment to produce a sense of flying.

Belladonna (which means beautiful woman) was used by women to dilate their pupils, to make them appear more alluring.

Medicine has found numerous uses for the toxins in Deadly Nightshade. Scopolamine is administered by eye surgeons to dilate pupils and to alleviate motion sickness. Hyoscyamine is employed in cases of irritable bowel syndrome, diverticulitis, colic and other inflammatory conditions of the GI tract. Belladonna toxins can help to control muscle spasms in cases of Parkinson's disease. When applied topically, belladonna is also quite effective in reducing pain, as in rheumatism, sciatica or neuralgia.

Hemlock

The association of hemlock (Conium maculatum ) with the death of Socrates has made this one of the most widely known botanicals in ancient medicine. In antiquity, people were familiar with hemlock and its poisonous applications. 

As an ancient medicine, hemlock has primarily been used for its sedative and antispasmodic properties. The plant was also used by Greek and Arab physicians to treat joint pain. 

Foxglove

Foxglove , or Digitalis purpurea, contains a group of compounds known collectively as Digitalin. These agents, also known as cardiac glycosides, are used to strengthen cardiac output, and as an anti-arrhythmic agent to control heart rate, notably in cases of atrial fibrillation.