dose; the ED 50 of a potent drug is lower than the ED 50 of a less potent drug. For example, it has been said that LSD is one of the most potent psychoactive drugs known. This is true in that hallucinogenic effects can be obtained with 50 micrograms (μg), compared with several milligrams (mg) required of other hallucinogens (a μg is 1/1,000 of a mg, which is 1/1,000 of a gram [g]). However, the effects of LSD are relatively limited—it doesn’t lead to overdose deaths the way heroin and alcohol do. Alcohol has a greater variety of more powerful effects than LSD, even though in terms of the dose required to produce a psychological effect LSD is thousands of times more potent.
Time-Dependent Factors in Drug Actions
In the mouse experiment, we picked one hour after administering the drug to check for the sleeping effect. Obviously, we would have had to learn a bit about the time course of the drug’s effect before picking one hour. Some very rapidly acting drug might have put the mice to on several groups of 20 mice each. Each group will receive a different dose, and an hour later we will check to see how many mice in each group are sleeping. Let us assume that at the lowest dose we tested, only 1 of the 20 mice was asleep, and at the highest doses all were asleep, with other values in between. By drawing a line through these points, we can estimate the dose required to put half of the mice to sleep (the ED 50 or the effective dose for 50 percent
