It's been known for more than 2,000 years that the bark of the willow tree has the power to relieve pain. The bark contains salicin, which is converted to salicylic acid in the body. Salicylic acid is closely related to Aspirin, which has become the most successful drug in history.

More than a trillion Aspirin tablets are consumed around the world every year, saving most of us the hassle of harvesting willow bark to treat our aches and pains.

Other plants that yield recognized medicines include:

• Deadly nightshade (Atropa belladonna), which contains the active ingredient atropine (used to accelerate a dangerously slow heart rate, dilates the pupil).
• Mandrake (Mandragora officinarum), which contains the active ingredient hyoscine (the earliest known general anesthetic).

Now research is suggesting it's not just plants that hold healing — or preventive — powers. Some common spices are turning heads as well.

Health Canada defines herbs as "the leaves, roots and flowers of plants grown and processed for culinary, cosmetic, industrial, medicinal, landscaping, decorative and fragrant purposes."

Spices, the agency says, "are seeds, root, bark and flowers of plants that are grown, harvested and processed for use as food or beverage flavouring." Some examples are caraway, coriander, dill and mustard.

A recent study found that turmeric, one of the spices that adds punch to curry, may also help relieve arthritis pain. Earlier research on rats suggested turmeric might prevent joint inflammation. Now researchers at the University of Arizona have looked at why an extract of the spice may be therapeutic.

"Just as the willow bark provided relief for arthritis patients before the advent of Aspirin, it would appear that the underground stem of a tropical plant [turmeric] may also hold promise for the treatment of joint inflammation and destruction," they concluded.

More than 100,000 women, men and children will be diagnosed with arthritis this year in Canada, according to the Arthritis Society.

Meanwhile, another recent study suggests curcumin — a component of curry and turmeric — may help the immune system get rid of the protein that builds up to form damaging plaques in the brains of Alzheimer's patients.

The findings complement previous research linking curry consumption to reduced Alzheimer's risk. One study found that in India — where curry is commonly used to spice food — only one per cent of the elderly developed the disease. That's one-quarter of the rate in North America.

Another study found that daily doses of curcumin may also reduce your risk of developing polyps in the colon, a known precursor to colon cancer.

The list of possibly therapeutic spices is a long one. Here's some of the common ones and the medicinal uses they are purported to have:

• Allspice: an aromatic stimulant, helps to relieve indigestion and gas.
• Anise: sweet and aromatic, with a hint of licorice flavour. Used to treat digestive problems and to relieve the pain of toothaches. Its essential oil is used to treat lice and scabies.
• Cardamom: strong, unique taste. Often used in Indian cooking and Scandinavian baking. Used medicinally to treat infections in teeth and gums, congestion of the lungs, and digestive disorders.
• Cayenne pepper: Increases metabolism and fat-burning ability by up to 25 per cent.
• Celery seed: Used as a homeopathic extract as a diuretic. Believed to help clear toxins from the system. Also used as a mild digestive stimulant.
• Chili powder: Relieves achy joints. Research shows that capsaicin, found in chili peppers, has an anti-inflammatory effect, which may help ease arthritic swelling and pain.
• Cinnamon: Often used to settle an upset stomach as well as a metabolism booster. May protect against Type-2 diabetes and heart disease. A 2003 study found that about half a teaspoon lowered blood glucose, cholesterol, and triglyceride levels.
• Coriander (also known as cilantro and Chinese parsley): Said to assist with clearing the body of lead, aluminum, and mercury. Also said to help relieve anxiety and insomnia.
• Garlic: Besides its mythical power to keep away vampires and werewolves, regular consumption of garlic is said to lower blood pressure and levels of bad cholesterol. Recent research has also found that it may help in the treatment of diabetes — and prevent flatulence.
• Ginger: Can inhibit nausea and vomiting that may accompany morning sickness or motion sickness.
• Horseradish: Used as a digestive stimulant.
• Licorice: In its powdered form, licorice root has been used as a cough remedy. Modern cough syrups sometimes include licorice extract as an ingredient.
• Mint: Traditionally, mint was used to treat stomach ache and chest pains. It is also a strong diuretic and digestive aid.
• Mustard: There are several kinds of mustard — not just the type you slather on your hot dogs and hamburgers. "Mustard packs" have been used for generations to help relieve respiratory problems.
• Rosemary: Acts as a stimulant and mild analgesic, and has been used to treat headaches and poor circulation.
• Saffron: Besides being the world's most expensive spice, saffron has been used to treat depression in Persian traditional medicine. A 2005 study found that saffron may help in cases of mild to moderate depression.
• Wasabi: A 2004 South Korean study suggests that wasabi may help prevent ulcers by killing some of the bacteria that cause ulcers. The hot paste may also prevent tooth decay.