Psychoactivity refers to the effects that certain substances have on the mind and behavior. These substances can alter mood, perception, and cognitive functions. Common examples include alcohol, caffeine, and psychoactive drugs like marijuana or LSD. The changes in mental state can range from mild relaxation to intense hallucinations. Psychoactive substances work by interacting with the brain's neurotransmitters, which are chemicals that transmit signals between nerve cells. This interaction can lead to various effects, such as increased energy, altered sensory experiences, or changes in emotional states. Understanding psychoactivity is important for both health and safety.