If you are thinking of trying an alternative treatment for seasonal allergies, you could run the risk of using a product that, at best, isn’t very useful and at worst, could aggravate your symptoms. We put four popular herbal remedies under the microscope and here's what we found.

Butterbur
One of the best-studied natural medicines for allergies, butterbur may ease hay-fever symptoms, possibly by reducing levels of histamines and leukotrienes, chemicals that can set off an allergic response. But the long-term safety of butterbur is unknown. And some preparations might also contain certain chemicals, called pyrrolizidine alkaloids (PAs), that can harm the liver and lungs. If you decide to try it, look for products containing at least 7.5 mg of petasin and isopetasin, the presumed active ingredients. And only use butterbur products that are labeled as free of PAs. Finally, steer clear of the herb if you're allergic to ragweed; it's related to that plant family and could produce an allergic response.

Echinacea
Though some research has suggested that this common herb acts as an anti-inflammatory, there's no solid evidence that it eases hay-fever symptoms. Echinacea might also interact with drugs that suppress the immune system, such as cyclosporine (Sandimmune and generic). People with an immune-system disorder should avoid it, as should those with ragweed allergies, because it’s also related to that plant family.

Grape-seed extract
Derived from parts of the grape plant, grape-seed extract is sometimes vaunted as a natural antihistamine. But it does not appear to quell hay-fever symptoms.

Stinging nettle leaf
Early evidence suggests that extracts of this plant might fight inflammation and modestly curb hay-fever symptoms. But it’s still too soon to tell, so don’t rely on it. Avoid stinging nettle if you’re diabetic; it might increase the effects of some diabetes medications. It might also decrease the effectiveness of the blood-thinning drug warfarin (Coumadin and generic).

Many experts recommend first trying better-established strategies to treat hay fever, such as avoiding the allergens that can cause reactions and taking prescription or over-the-counter allergy medication, which both have a fairly reliable track record. And remember, there is little government oversight of the potency, purity, and identity of supplements, compared to that of prescription and over-the-counter drugs (see "Five steps to choosing a nutritional supplement"), so, in general, exercise caution. That applies especially to young children. And avoid taking them if you are pregnant.

For more information, see our free Best Buy Drugs report on allergy treatments, and read our complete ratings on Natural Medicines (subscribers only).