Found in coffee, tea, colas, chocolate, as well as some medicines, caffeine is considered safe for adults -- excluding women who are pregnant and of childbearing age -- when consumed in moderation, or under 400mg per day, reports Health Canada. However, because each person responds differently to caffeine, it can have positive and negative effects on health. Factors that make you more sensitive to its negative effects include not regularly consuming caffeine, body mass, age, smoking habits, drug or hormone use, stress, health conditions and being male, Health Scout says.
Increased Alertness and Restlessness
Caffeine's effects can begin as soon as 15 minutes after ingestion, Health Scout says. Though most people know that caffeine helps as an energy boost, relieving fatigue and drowsiness, taking in too much can have undesired effects. MedlinePlus says that too much caffeine can lead to jitters, or muscle tremors, restlessness, and even anxiety. For those who are more sensitive to caffeine, these negative effects can occur with smaller amounts.
Unrestful Sleep and Insomnia
Because caffeine remains in the body for hours -- approximately half is eliminated in the only first six hours -- taking in caffeine too late in the day could extend the time necessary to pass from early slumber to deep sleep. Therefore, drinking coffee to eliminate midday sleepiness can also lead you being wide awake at 10 p.m., reports Health Scout. Drinking more than the recommended daily amount exacerbates these effects.
Elevates Heart Rate
No studies have yet linked caffeine use to cardiovascular disease. However, caffeine is known to elevate heart rate. This effect can be important to note for users prone to anxiety.
Caffeine Intoxication and Addiction
Caffeine is by definition a drug, working as a central nervous system stimulant. As a result, it can be toxic in large amounts. MedlinePlus says that for those who are addicted, abrupt withdrawal can cause headaches, drowsiness, irritability, nausea, vomiting, and other symptoms.
In some cases, caffeine has been known to cause gastrointestinal problems and headaches, the Mayo Clinic says. Without proper calcium balance, long-term caffeine use can affect bone health -- for example, bone density and the risk of fractures. Most important, caffeine can interact with many drugs, so Health Scout recommends consulting your doctor or pharmacist before taking new medications. Caffeine has proven for some as an effective treatment for migraines. As a diuretic, caffeine can cause excessive urination. It also functions as a mild appetite suppressant.