Yes you can. Side effects of over-consumption include nervousness, insomnia, and tremors. Excessive caffeine consumption can produce overly rapid heartbeat, mental stress, gastric discomfort and anxiety. The human lethal dose of caffeine is equal to approximately 66 five-ounce cups of coffee. Some people do not tolerate caffeine. If caffeine makes you jittery, sweaty, sick or uncomfortable, then it isn’t your drug.