Most energy drinks contain large amounts of caffeine, which can provide a temporary energy boost. Some energy drinks contain sugar and other substances. The boost is short-lived, however, and may be accompanied by other problems.

For example, energy drinks that contain sugar may contribute to weight gain — and too much caffeine, or caffeine-like substances, can lead to:

• Nervousness
• Irritability
• Insomnia
• Rapid heartbeat
• Increased blood pressure

Mixing energy drinks with alcohol may be even more problematic. Energy drinks can blunt the feeling of intoxication, which may lead to heavier drinking and alcohol-related injuries.

For most people, occasional energy drinks are fine, but the amount of caffeine can vary from product to product. Try to limit yourself to no more than 400 milligrams of caffeine a day from all sources.

Energy drinks are not recommended for children and adolescents. Pregnant women and women who are breast-feeding may want to avoid or limit consumption of these beverages. If you have an underlying condition such as heart disease or high blood pressure, ask your doctor if energy drinks may cause complications.

If you're consistently fatigued or run-down, consider healthier ways to boost your energy. Get adequate sleep, include physical activity in your daily routine, and eat a healthy diet. If these strategies don't seem to help, consult your doctor. Sometimes fatigue is a sign of an underlying medical condition, such as hypothyroidism or anemia.