Final answer:
Psychoactive drugs are substances that affect brain chemistry and are used for medical, ritual, and recreational purposes. They can act as agonists or antagonists. Examples of legal psychostimulants are methylphenidate and amphetamines.
Step-by-step explanation:
Psychoactive drugs are substances that affect brain chemistry and are used for various purposes, including medical, ritual, and recreational uses. They can act as either agonists, enhancing the activity of neurotransmitters, or antagonists, decreasing the activity of neurotransmitters. Two legal psychostimulants are methylphenidate, commonly used to treat ADHD, and amphetamines, which are used to treat attention deficit disorder.