When the staff goes to tranquilize Betty, the nurse says the syringe contains 25 cc. The syringe is clearly much smaller than that, containing probably about 3-4 cc of liquid.
Parathion is an insecticide not an amphetamine as portrayed in this episode. It's highly toxic and has been banned or restricted in most countries.
The shot given to Betty was said to be 25 cc of some tranquilizer. Virtually all tranquilizers are effective in very small amounts. 25 cc of any tranquilizer in a ~150 lb human would kill in seconds.