Pharmaceutical giants pour billions into inventing new, blockbuster drugs. But there's one big challenge they can't seem to crack: Ensuring that patients actually take their medications.

Just half of those given a prescription to prevent heart disease actually adhere to refilling their medications, researchers find in the Journal of American Medicine. That lack of compliance, they estimate, results in 113,00 deaths annually.

More from Kerry Grens on why adherence tends to be so low:

In some cases, it could be related to the patient - difficulty reading the drug label or opening the container, fear of side effects, or challenges making it to the pharmacy for a refill.

The health care system could play a role too.

"It's difficult to have real a discourse with a physician because... everybody's busy," David Blackburn [a researcher not involved with the study] told Reuters Health. "Because of the system and the constraints on cost and time, I think what you end up with are people who are really inadequately prepared" to follow through with their prescriptions.

Numerous studies have also found the cost of medication to be a factor, too, with some not adhering to a drug regimen because it was financially out of reach.