The active ingredient in Roundup is glyphosate, a broad-spectrum herbicide that kills nearly any plant it touches. Glyphosate has been Roundup’s signature ingredient since Monsanto introduced the product in 1974. However, if you’re buying Roundup off the shelf at a hardware store today, there’s a good chance your bottle contains something else entirely. Bayer, which now owns the Roundup brand, has phased glyphosate out of its consumer product line while keeping it in professional and agricultural formulations.
How Glyphosate Kills Plants
Glyphosate’s chemical name is N-(phosphonomethyl)glycine. It works by blocking a specific enzyme that plants need to produce certain amino acids, the building blocks of proteins. Without those amino acids, the plant can’t synthesize the proteins it needs to grow, and it dies. This enzyme pathway exists in plants but not in mammals, which is one reason glyphosate was considered relatively low-risk when it first came to market.
Glyphosate is non-selective, meaning it doesn’t distinguish between a dandelion and a tomato plant. Anything green that absorbs it will be affected. That’s why traditional Roundup was never meant for use on lawns or around desirable plants. It was designed to clear everything in a targeted area.
What’s Actually in the Bottle Now
If you pick up a bottle labeled “Roundup” at a garden center today, the active ingredient depends entirely on which product you’re looking at. The Roundup brand now covers a wide lineup of consumer formulas, most of which no longer contain glyphosate. Bayer phased glyphosate out of its residential products following thousands of lawsuits alleging the chemical caused cancer. Professional-grade Roundup products used in agriculture and landscaping still contain glyphosate.
Here’s what’s in the most common consumer versions:
- Roundup Dual Action Weed and Grass Killer: A mix of four active ingredients: triclopyr (targets broadleaf plants), fluazifop (targets grasses), diquat (a fast-acting contact herbicide), and imazapic (provides pre- and post-emergence weed control).
- Roundup for Lawns: A combination of MCPA, quinclorac, dicamba, and sulfentrazone. These are selective herbicides, meaning they kill weeds without killing lawn grass. Quinclorac specifically targets crabgrass, while dicamba and MCPA mimic natural plant hormones to disrupt broadleaf weed growth.
- Roundup Crabgrass Destroyer: Contains topramezone, which targets grassy weeds and some broadleaf weeds.
- Roundup Poison Ivy and Tough Brush Killer: Uses triclopyr as its primary active ingredient, targeting woody plants and broadleaf species while leaving grasses relatively unharmed.
This means two neighbors could both be spraying “Roundup” with completely different chemicals. Always check the active ingredient panel on the label rather than relying on the brand name.
Concentration in Glyphosate Formulas
For professional and agricultural products that still use glyphosate, the concentration varies significantly by format. A super concentrate formulation contains about 50% glyphosate (as its isopropylamine salt form), with the other 50% being water, surfactants, and other inactive ingredients. Ready-to-use spray bottles come pre-diluted to much lower concentrations. Concentrated products are meant to be mixed with water before application, while ready-to-use versions go straight from the bottle to the sprayer.
The Role of Surfactants
Glyphosate on its own doesn’t penetrate plant leaves very well. That’s why Roundup formulations have always included surfactants, chemicals that help the herbicide spread across and soak into the waxy surface of leaves. The most well-known surfactant in traditional Roundup is polyethoxylated tallow amine (sometimes called POEA). This compound works by reducing the surface tension of the spray droplet, allowing it to spread evenly over the leaf rather than beading up. It also helps glyphosate pass through the leaf’s outer waxy layer so it can enter the plant’s vascular system.
These surfactants have drawn their own scrutiny. Some research has found that the surfactant component can be more toxic to aquatic organisms than glyphosate itself, which is why certain glyphosate products designed for use near water are formulated without POEA.
The Cancer Debate
Glyphosate’s safety profile has been one of the most contentious topics in pesticide regulation. In 2015, the International Agency for Research on Cancer (IARC), a branch of the World Health Organization, classified glyphosate as “probably carcinogenic to humans.” That classification triggered a wave of lawsuits and public concern.
The U.S. Environmental Protection Agency reached a different conclusion, finding that glyphosate is “not likely to be carcinogenic to humans.” The EPA noted that it reviewed a significantly larger dataset than IARC, including 15 animal carcinogenicity studies compared to IARC’s eight. The EPA’s position aligns with assessments from the European Food Safety Authority, the European Chemicals Agency, the Canadian Pest Management Regulatory Agency, the Australian Pesticide and Veterinary Medicines Authority, and regulators in Japan and New Zealand.
Despite the regulatory consensus, Bayer has paid billions to settle lawsuits from plaintiffs who developed non-Hodgkin lymphoma after long-term glyphosate exposure. The decision to remove glyphosate from consumer products was largely a response to this litigation rather than a regulatory mandate.
Glyphosate’s Regulatory Status Worldwide
Glyphosate remains legal in most major markets. The European Union renewed its approval through December 2033, though with restrictions. EU rules prohibit using glyphosate as a desiccant (spraying it on crops right before harvest to speed drying), and individual EU member states can impose additional limits within their borders. Several countries and municipalities have restricted or banned glyphosate use in public spaces like parks and playgrounds, but outright national bans remain rare among major agricultural economies.
In the United States, glyphosate is fully registered for both agricultural and residential use, though as noted, Bayer has voluntarily removed it from consumer Roundup products. Farmers and licensed applicators continue to use glyphosate-based Roundup formulations on a massive scale, particularly on crops genetically engineered to tolerate the herbicide.