Light, air and moisture all speed the deterioration of dried plants and rob them of their usefulness. So when you buy herbs, you want to buy preparations that are A standardized extract is one that has been assayed to determine the content of one or several key constituents. The label will give a percentage content of these compounds. Standardization is the best assurance that a product contains what it's supposed to contain in amounts sufficient to produce a desired effect. Standardized extracts may be liquids or solids.
Tinctures are liquid extracts of fresh or dried plants in alcohol.
The alcohol content is high enough to preserve the plant material. Tinctures are stable and convenient, but their quality is only as good as that of the herbs that went into them. If you don't want the alcohol, you can look for other liquid extracts of herbs in vinegar or glycerin, but these are not as good as alcohol-based products. Or you can buy your herbs freeze-dried. This process removes the solvents.