What are the effects of stimulants and depressants on heart rate and breathing rate?

Stimulants, such as caffeine and amphetamines, typically increase heart rate and breathing rate by stimulating the central nervous system, leading to heightened alertness and energy. In contrast, depressants, like alcohol and benzodiazepines, generally slow down these functions, resulting in a decreased heart rate and reduced breathing rate as they induce relaxation and sedation. The overall impact of these substances can vary based on dosage and individual response.