Cannabis has a chemical constituent called tetrahydrocannabinol (THC), responsible for its characteristic short term effects:

• Muscular relaxation that can cause loss of coordination and balance as well as increasing the reaction time to stimuli
• Decreased muscle strength and slight drowsiness
• Dilation of blood vessels that manifests in the red eyes
• Increased pulse and heart rate
• Dry mouth and less saliva
• Coughing and irritation
• Occasionally, it may cause negative reactions of panic and terror.

It can also cause lack of motivation, characterized by loss of interest in social relationships and activities, and a generally passive attitude toward others.