Studies Show Caffeine’s Dual Nature

Cons

Mild Addiction
When caffeine lovers don't receive enough of what their bodies are used to, they can develop feelings of irritability, anxiety, or fatigue. And some caffeinated foods aren't even labeled as such; one cup of coffee-flavored yogurt can have the same caffeine as a full cup of coffee or have no caffeine at all. Knowledge of what you're consuming and moderation in consumption are keys to good health.

Sleeplessness
Drinking one or two cups of coffee before 4 pm generally shouldn't ruin a good night's sleep. But caffeine intake throughout the day can lower the number of minutes you sleep at night, even if you don't remember waking. Caffeine seems to affect individuals' sleep patterns in various ways. Some coffee aficionados may crash once they stop consuming caffeine; others complain of insomnia.

Not Useful For Weight Loss
Although caffeine perks you up and gives you energy, a wide-ranging, long-term study has found that it doesn't seem to add up: some people even gain weight as they increase caffeine use.