One of the most effective of all natural antihistamines, stinging nettle, grows as a common weed throughout the United States. An extract from the leaves is made into capsules available at health food stores and can also be purchased as a tincture or a tea. Be careful about coming into contact with fresh stinging nettle which, true to its name, will cause painful skin inflammation.
The recommended dose is 300 milligrams daily. While only effective for a few hours, stinging nettle has none of the groggy, unpleasant after effects of over-the-counter or prescription antihistamines.
In Europe, butterbur is becoming increasingly popular as a natural antihistamine, particularly for hayfever. Although not easy to find in the United States, it can be purchased online. Traditionally goldenseal has been used for the same purpose, but there are no studies verifying its effectiveness like those that have been conducted with stinging nettle and butterbur.
Some Words of Caution
The market is rife with gadgets and concoctions reported to naturally combat allergies. Expensive air cleaning units do a landmark business, but controlled studies have shown that they are ineffective in reducing symptoms once an attack has been triggered. So, unless you intend to sit in front of the unit for the duration of allergy season, don't bother. You'd be better served by wearing a paper filtration mask outdoors on high pollen days. Most area news stations in their broadcasts and on their websites now helpfully supply pollen counts for the day.
It's important to remember the words "natural" and "safe" are not necessarily synonymous. Take supplements at the recommended dosage only and discontinue immediately if any side effects are felt. Also, if you take prescription medication for other conditions, always research possible toxic interactions before starting on a supplement.