That is, if you take a cyanide pill, how long until you are dead without any reasonable hope of revival? The spy suicides on TV don't seem very realistic but I could be completely wrong.
15-25 minutes depending on the amount of food in the persons stomach
it depends on the concentration of the cyanide and the form of introduction into your body.
what makes cyanide so notorious is the speed that it acts. Cyanides are amoungst the most fast acting poisons known, mainly sodium cyanide and potassium cyanide as well as hydrogen cyanide.
As a hyperthetical example, if you wanted to kill yourself, you wouldn't bother weighing out the toxic dose, you would just get a tea spoon full and dissolve it in water and swallow it down. A rounded teaspoon of potassium cyanide would hold about 50 times the amount needed to kill you.
Upon swallowing such a solution, you would collapse almost immediately and loose consiousness within 10-20 seconds. Death would follow in a matter of minutes from cardiac arrest.
With such a massive dose taken, any medical assistance no matter how aggressive would prove futile.
It depends on the dosage. And it depends on the compound. Potassium cyanide has a different mg/kg ratio than hydrogen cyanide. Hydrogen cyanide is a gas and potassium cyanide is a salt. sodium cyanide is another salt. Different mg/kg ratios...mg / kg is mg potassium cyanide / kg body weight
So... looking a KCN...the oral LD-Lo for KCN in humans is 2.857 mg/kg. The oral LD-50 for KCN in rats and rabbits is about 5 mg/kg. Best guess is that the LD-50 for humans is probably comparable to that of rats and rabbits.
LD-Lo is the lowest known concentration that has resulted in death. LD-50 is the concentration for which 50% of the test population is killed. But those numbers do not include medical intervention.
So what happens with cyanide is that it is preferentially bound to the hemoglobin in your blood. That is the molecule in your blood that is responsible for oxygen transport. Meaning cyanide poisoning essentially results is asphyxiation.
Within minutes after consuming a lethal dosage, you have difficulty breathing. Then you pass out, then after another 5 minutes or so, your brain begins to die. And then your heart muscle begins to die and your heart stops beating. In the mean time, your body undergoes seizures, you probably vomit and your skin turns pink to cherry red.
Doses below the LD-Lo will result in extreme headaches, nausea, vertigo, etc but are survivable with little long term effects. Your body is capable of metabolizing the CN- ion and excreting it.
Medical treatments are available for poisoning and must be administered immediately (within minutes for dosages > lethal) as you can imagine.
is a tsp full lethal?
1 tsp x (5 mL / tsp) x (1.595g/mL) = 7.975g NaCl
1 tsp x (5 mL / tsp) x (1.52g/mL) = 7.6g KCl
typical body weight = say.. 60 kg
typical lethal dose for an average human....
60kg x (3.7 mg NaCN / kg) x (1g / 1000mg) = 0.2g KCN
60kg x (5 mg KCN / kg) x (1g / 1000mg) = 0.3g KCN
of course it is..
how big would a capsule need to be to ensure killing a...200lb male? like in the movies?
200lb x (1kg / 2.2lbs) x (3.7mg NaCN / kg) x (1g / 1000mg) x (1 mL / 1.595g) = 0.2 mL minimum.
200lb x (1kg / 2.2lbs) x (5mg NaCN / kg) x (1g / 1000mg) x (1 mL / 1.52g) = 0.3 mL minimum.
0.2 mL x (1 cm^3 / 1mL) x (10 mm / 1 cm)^3 = 200 mm^3
that means you would need...
a NaCN capsule about 4mm in diameter and 16mm in length
a KCN capsule about 4mm in diameter and 24mm in length.
in comparison...That would be about the size of 2/3 of an inch of a pencil for NaCN and 1 inch for KCN and since that would be the mininum dosage to ensure death. So you'd probably want to take two. Maybe three.
So no. The movies that depict a person biting a tiny pill and droping dead instantly are not accurate.