Is sodium cyanide harmful for human beings?

Quite much so!

It is extremely dangerous.

Not only to human beings. Most living organisms suffer great adverse effects from this and a quick painfull death is most certain with too much of it.

Cyanide salts are among the most rapidly acting of all known poisons. Cyanide is a potent inhibitor of respiration, acting on mitochondrial cytochrome oxidase and hence blocking electron transport. This results in decreased oxidative metabolism and oxygen utilization. Lactic acidosis then occurs as a consequence of anaerobic metabolism.

However:

Sodium Cyanide have been utilized as a drug for cancer (with positive results however some contradictions)

Cyanide as in Vitamin B17 may have a most positive effect on cancer and has proven to extend life expectancy in terminal ill patients.

Edgar Cayce recommended eating three raw almonds a day (for their cyanide content) as a means of cancer prevention in healthy patients.

The theory is that Cyanide found in some kernels (Apricot kernels) is surrounded by sugar. As cancer cells are high consumers of sugar, they eat the sugar and release the cyanide, hence killing them self in this process of being "greedy".

We can not dismiss the positive effect of certain poisons when used "correctly".

All substances are dangerous in too large quantities. Even water.

Botulinum Toxin is so dangerous that only 270 nano grams is enough to kill an adult. Still this toxin have found its way into medical use. "Botox" is injected by many people today so that they can look younger even at an "old" age.

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