Home » Module 5: Why Do Plants Make Drugs for Humans? » Content Background: Plants are Excellent Sources of Drugs

Content Background: Plants are Excellent Sources of Drugs

Many plants contain chemicals that can be used as drugs1. For example, cocaine is derived from the coca plant (erythroxylon coca), nicotine from the tobacco plant (nicotiana tabacum), THC (9-tetrahydrocannibinol) from the marijuana plant (cannabis sativa), morphine from the opium poppy plant (papaver somniferum), and salicylic acid (the precursor to aspirin) from the bark of the willow tree (salix nigra) (Figure 1). In many cases, the active ingredient in the plant affects behavior or mood; we call this effect in the brain a psychoactive effect2. Cocaine, morphine, THC, and nicotine, all have psychoactive properties. On the other hand, aspirin, like salicylic acid, does not have psychoactive properties; its analgesic effect (reducing pain) does not involve changes in behavior or mood. Similarly, digoxin, the active ingredient in the foxglove plant, is still used today to treat heart rhythm disturbances and congestive heart failure. It gets into the brain, but it has no psychoactive properties.

Figure 1 The leaf structure is shown for several plants that contain compounds used as drugs.

1 a substance that affects the structure or function of a cell or organism.
2 pertains to drugs that act in the brain to produce changes in mood, perceptions and behavior.