Caffeine- The bitter, white crystalline xanthine alkaloid caffeine is found in tea, coffee, soft drinks, chocolates, pain relievers, and a variety of over the counter medications. It is a psychoactive stimulant drug that causes increased alertness by stimulating the central nervous system. For the same reason, many people feel more energetic after consuming it. It even elevates the mood but these effects do not last for long. The effects of caffeine usually last for about five to six hours, though caffeine sensitivity varies from person to person. It has been found that people who consume lot of caffeine on a daily basis soon develop less sensitivity and may need to increase their intake to enjoy the same effect. Being a diuretic, a person consuming caffeine may have to urinate more often.