The exam is paid for by the insurance company.
Usually, if you are over age 30 or requesting $100,000 or more of life insurance, a medical exam may be required.
The insurance company uses the information from the exam to determine your health, expected longevity (how long you may live), and if you use any tobacco or drugs.
The medical exam may ask additional health questions about your and your family's health history. In addition, they may require a blood or urine sample to check your cholesterol and protein levels, if you have AIDS/HIV, STD's, alcohol or drugs in your system including but not limited to marijuana, cocaine, methamphetamine, etc.
If you do have any illegal drugs in your system you will likely be turned down for coverage.
If you answered no on the application regarding use of tobacco, and you were found to have tobacco in your system, you may have your life insurance quote re-rated, based on tobacco use.
Here's how you can learn more about life insurance drug tests and how they work.