Hemp Nettle Allergy: Not Hemp, Not Nettle — But Still a Real Fall Allergen

No — hemp nettle (Galeopsis tetrahit) is related to neither cannabis nor stinging nettle despite carrying both words in its common name. Galeopsis belongs to family Lamiaceae, the mint family, making it a botanical relative of basil, oregano, lavender, and catnip. Cannabis sativa belongs to family Cannabaceae, and stinging nettle (Urtica dioica) belongs to family Urticaceae — completely different plant families with no allergological cross-reactivity to hemp nettle. The name 'hemp nettle' is a double misnomer that reflects the plant's visual resemblance to both nettles (opposite leaves, square stems) and the growth habit of hemp in disturbed habitats, not any taxonomic or allergen relationship. Patients sensitized to hemp nettle pollen are not at increased risk from cannabis, hemp seeds, or stinging nettle exposure.

No — hemp nettle (Galeopsis tetrahit) does not have stinging hairs and will not cause the urticarial sting reaction associated with true stinging nettle (Urtica dioica). Stinging nettle's urticating reaction is caused by silica-tipped hollow trichomes that inject a mixture of histamine, serotonin, acetylcholine, and formic acid on skin contact. Hemp nettle lacks these specialized trichomes entirely. While hemp nettle has hairy stems that superficially resemble stinging nettle, the hairs are simple non-stinging plant hairs. You can handle hemp nettle without any skin reaction. The allergy risk from hemp nettle is respiratory — from inhaling its wind-dispersed pollen — not dermal from plant contact.

Hemp nettle blooms from July through September across its northern US and Canadian range, making its pollen season occur in the gap between the main grass pollen season (which typically ends in July) and the peak ragweed and fall weed season (which peaks mid-August to October). This intermediate timing means hemp nettle symptoms may be underrecognized — patients may assume their summer allergy season has ended after grass pollen declines, not realizing that summer weeds like hemp nettle are beginning their bloom. In cooler northern climates such as the Pacific Northwest, Great Lakes region, and New England, peak bloom occurs in August. Earlier frost terminates the season by late September or October.

Commercial expanded weed pollen panels often include clinically relevant regional allergens based on patient symptom correlation data, even when those allergens have not yet had molecular proteins formally characterized and registered with WHO/IUIS. Hemp nettle (Galeopsis tetrahit) produces wind-dispersed pollen in northern US regions, and patients in those regions have reported positive skin prick test results and IgE responses to crude G. tetrahit pollen extract concurrent with late-summer weed season symptoms. This clinical evidence is sufficient for inclusion on a panel even absent formal molecular allergen characterization. The extract used is a non-standardized crude pollen preparation, and results should be interpreted in the context of symptom timing and confirmed by an allergist.

There is no documented food cross-reactivity between hemp nettle (Galeopsis, Lamiaceae) pollen sensitization and culinary Lamiaceae herbs such as basil, oregano, mint, thyme, rosemary, or lavender. While botanical family membership implies shared protein families at a structural level, IgE-mediated cross-reactivity requires sufficient sequence identity in the specific epitopes recognized by allergy antibodies — and this has not been demonstrated between Galeopsis pollen proteins and Lamiaceae food herbs. If you are sensitized to hemp nettle pollen and experience any oral symptoms after consuming mint-family herbs, report this to your allergist for specific IgE testing of the relevant herbs rather than assuming cross-reactivity based on family membership alone.

Hemp nettle is plausible as an asthma trigger in sensitized patients during the July through September bloom period in northern US regions, following the same mechanism as other aeroallergen-induced asthma: airway IgE sensitization with mast cell degranulation and eosinophilic inflammation on pollen exposure. Direct evidence from hemp nettle-specific asthma studies is limited given the absence of characterized allergens, but the general principle that seasonal aeroallergen exposure triggers asthma in sensitized individuals applies. Patients with asthma who notice mid-summer July or August worsening that does not correspond to either grass pollen or ragweed season timing should discuss expanded summer weed panel testing with their allergist, including hemp nettle if they are in a northern US or Canadian region where the plant is prevalent.

Identifying hemp nettle as the specific trigger for summer weed pollen symptoms requires combining three elements: temporal symptom correlation (symptoms consistently worsen in July and August), geographic exposure (you live in or visit northern US or Canadian regions where hemp nettle grows), and a positive test result on an expanded weed panel that includes G. tetrahit extract. Because no standard ImmunoCAP code exists for hemp nettle, testing availability varies by allergist and laboratory. A board-certified allergist with access to an expanded regional panel can confirm sensitization while also ruling out pan-allergen cross-reactivity as a confounding factor. Clinical correlation between symptom timing and hemp nettle bloom in your region is a critical interpretive element.

Hemp nettle (Galeopsis tetrahit) and white dead-nettle (Lamium album) are both Lamiaceae weeds that mimic stinging nettle's appearance without producing any sting — but they are different genera with distinct identifying features. Hemp nettle grows 1 to 3 feet tall, is annual, has distinctive swollen stem nodes at the point where leaves attach, and bears pink or purple-white flowers with a toothed calyx. White dead-nettle is smaller (6 to 18 inches), is perennial, has smooth (not swollen) stem nodes, and bears pure white hooded flowers — the classic bilabiate lip shape typical of Lamiaceae. Hemp nettle prefers cooler northern habitats; dead-nettle is more shade-tolerant and has a northeastern US distribution. Neither has characterized pollen allergens, but they appear on different allergy panels covering different regional distributions.

A standard blood test for hemp nettle allergy is not universally available because no ImmunoCAP code exists for Galeopsis tetrahit. The standard ImmunoCAP system used by most US clinical laboratories does not include a hemp nettle entry. Testing for hemp nettle IgE is possible through some specialty reference laboratories and expanded regional allergy panels that use non-standardized G. tetrahit crude pollen extract for their assays. Availability varies by laboratory and by geographic region — panels designed for northern US and Canadian allergy patterns are more likely to include G. tetrahit than standard national panels. An allergist familiar with regional pollen patterns in your area can direct you to the appropriate expanded panel for summer weed sensitization evaluation.

Yes, custom sublingual immunotherapy (SLIT) drops can include non-standardized Galeopsis tetrahit extract for patients with confirmed hemp nettle sensitization, where the extract is available through the compounding pharmacy's allergen sourcing. Because no FDA-approved SLIT tablet exists for hemp nettle or any Lamiaceae weed, immunotherapy is delivered as off-label custom-compounded drops or subcutaneous allergy shots. Hemp nettle sensitization is commonly treated as part of a broader summer weed pollen formulation that may include wormwood, English plantain, dock, and other co-sensitized July through September allergens in a single daily drop regimen. The 3 to 5 year SLIT course builds immune tolerance progressively, with seasonal symptom improvement typically beginning in the first or second treated summer.