They say that laughter is the best medicine, but some people might endorse chocolate instead.

The dark variety has been shown to reduce blood pressure better than a placebo. Scientists credit the flavanols in dark chocolate—they are thought to stimulate the production of nitric oxide, which helps relax the arteries so that blood can flow smoothly.

So if your doctor prescribed a daily dose of dark chocolate to keep hypertension at bay, would your first instinct be to head straight to Costco and buy a case of candy bars? Those who answered "yes" might get stuck with leftovers, Australian researchers are warning this week in the British Medical Journal.

Karin Ried and her colleagues from the University of Adelaide have spent a good amount of time investigating chocolate's ability to treat hypertension. One of their studies found that dark chocolate worked better than a placebo at getting systolic blood pressure below 140 mm Hg (low enough to qualify as prehypertensive) and diastolic blood pressure below 80 mm Hg (the top end of the normal range).

Another study
compared the ability of dark chocolate and a tomato extract pill to reduce blood pressure among people classified as prehypertensive. It turned out that neither worked better than a placebo, but the researchers reported a startling finding: Some people didn't like taking chocolate as medicine.

Yes, you read that correctly—it is possible to get sick of chocolate.

While 100% of study participants said they would be willing to keep on taking the tomato extract pill every day, only 73% said the same for dark chocolate. The chocolate used in the study came from a high-end chocolatier and was made with 70% cocoa, yet two people actually withdrew from the study because they found the candy "unpalatable."

Taste wasn't the only problem, the researchers found. Other reported side effects included headaches and constipation.

And of course, there were worries about the fat and calories. Study volunteers were prescribed 50 grams of dark chocolate a day. That is the equivalent of 1.2 regular-sized bars of Hershey's Special Dark, which pack 220 calories and 14.6 grams of fat, according to nutritional information provided by Hershey's.

So Ried and colleagues weren't too sweet on the idea—floated last month in BMJ—that dark chocolate could be a suitable treatment for high blood pressure. Based on their own findings, they wrote in a letter published online Wednesday afternoon, "the practicability of chocolate as a long-term treatment is debatable."