Amygdalin and laetrile are the same substance. Amygdalin = almonds. It was isolated by chemists almost 2 centuries ago from the bitter almonds (Prunus amygdalus), but it’s also present in the seeds of apricots (Prunus armeniaca) and black cherries as well (Prunus serotina).
As some might think this is a vitamin, it’s most certainly NOT, nor is it necessary for everyday health. But it is definitely a killer.
Proof of it’s poisonous effects are not a necessity. They have been known to every single one of the patients that used them as a cure. In the year of 1981, it was all over Mexico, as every other country banned the usage of laetrile.
So the question is – Why is it poisonous? Simple. Because it releases CN, combining it with H (hope you know chemistry well enough to know what those letters mean!) and finally making HCN (hydrogen-cyanide), which is a classic poison. It most often attacks the hemoglobin, leading to death and the decrease in numbers of enzymes.
Clinical researches were conducted in the US from 1978 to 1982 (http://www.cancer.gov/about-cancer/treatment/cam/hp/laetrile-pdq#section/all), and they were cancelled, because there was no solid evidence.
There was no sign of laetrile being a useful cure, but there were information that when you take the cure through an injection, the cyanide levels don’t grow as fast, but when you consume them normally, they grow drastically, to the point where people end up being poisoned. And that’s what bitter almonds can do. The conclusion is that somewhere in the human’s body lies an enzyme that releases cyanide – glucosidase, found in E. coli. That enzyme can be found in any laetrile containing seeds, but some vegetables as well – celery and carrots.
The actor Steve McQueen was on a treatment in the year of 1980 in Mexico, when he died. Is there a cure that can kill cancer cells with a selective method, without damaging the host? Certainly. That’s why the chemistry of natural products is popular these days.
The amount of cyanide in blood can depend on the seeds themselves, or whether the human being consuming them is a child, an adult, or a smoker. There are thousands of factors that can explain how somebody dies from seeds, and how somebody doesn’t.