Wakey Wakey: Sleeping in on the weekend makes it harder to get up on Monday. Photo by Tim Roberts/Getty Images

It’s not necessarily laziness that makes people hit the “snooze” button in the morning. Most likely, your body clock is mismatched with the demands of your life.

Your clock is controlled by the suprachiasmatic nucleus, a part of the brain that controls the body’s biological rhythms. But, says Jean Matheson, a sleep-disorders specialist at Beth Israel Medical Center in New York, these preset natural rhythms often don’t align with daily realities—work or school start times cannot be adjusted to fit a person’s sleep schedule. People who have trouble crawling out of bed probably have an inner clock set to late wake-up and sleep times, a condition known as phase delay.

It is possible to adjust your phase-delayed body clock, Matheson says, but at a price: No sleeping in on the weekends. “When people sleep late on weekends, they revert to their natural phase-delayed rhythm,” she explains. This makes it harder to wake up early on weekdays. You can train yourself to wake up earlier, Matheson says, by setting your alarm 15 minutes earlier each day (and heeding its call).

Exposure to artificial light in the evening can also cause phase delay. The brain is very sensitive to light, and too much of it just before bed—from computer screens, televisions or bright reading lights—can trick the brain into thinking it’s daytime.

If you find it difficult to adjust your sleep habits, there’s some good news. Scientists at the University of California at Irvine recently discovered that a single amino acid regulates your internal clock. One day, says pharmacology professor Paolo Sassone-Corsi, this research could translate into a drug that controls the brain’s sleep cycle.