Strychnine ((British, U.S.), /-naɪn/ or /-nɪn/ (U.S.)) is a very toxic (LD50 = 10 mg approx.), colorless crystalline alkaloid used as a pesticide, particularly for killing small vertebrates such as birds and rodents. Strychnine causes muscular convulsions and eventually death through asphyxia or sheer exhaustion. The most common source is from the seeds of the Strychnos nux vomica tree. Strychnine is one of the most bitter substances known. Its taste is detectable in concentrations as low as 1 ppm.
Although it is best known as a poison, small doses of strychnine were once used in medications as a stimulant, a laxative and as a treatment for other stomach ailments. A 1934 drug guide for nurses described it as "among the most valuable and widely prescribed drugs". Strychnine's stimulant effects also led to its use historically for enhancing performance in sports. Because of its high toxicity and tendency to cause convulsions, the use of strychnine in medicine was eventually abandoned once safer alternatives became available.
The dosage for medical use was cited as between "1/60th grain–1/10th grain", which is between 1.1 milligrams and 6.4 milligrams in modern measures. Normally the maximum dosage used was 3.2 mg, half of a "full dose". A lethal dose was cited as 1/2 a grain (32 mg), but people have been known to die from as little as 5 mg of strychnine.