Yerba mate isn’t inherently dangerous for most people, but it carries a few real risks worth understanding. The biggest concern, esophageal cancer, turns out to be more about how it’s traditionally consumed than the drink itself. Beyond that, its high caffeine content, potential to interfere with iron absorption, and rare liver effects round out the picture.
The Cancer Link Is About Temperature, Not the Drink
For years, researchers noticed higher rates of esophageal cancer in South American populations that drink yerba mate daily. The initial suspicion fell on polycyclic aromatic hydrocarbons (PAHs), cancer-linked compounds created when the leaves are smoke-dried during processing. Smoked commercial yerba mate contains roughly 1,700 nanograms per gram of PAHs, compared to about 620 ng/g in unsmoked versions. That sounds alarming, but the science has shifted considerably.
A comparative risk assessment published in BMC Cancer found that PAH exposure from mate posed negligible cancer risk, with safety margins over 100,000 times the threshold of concern. The real culprit is temperature. Traditional mate is consumed at scalding temperatures through a metal straw (bombilla) that delivers near-boiling liquid directly to the throat. The safety margin for very hot drinking temperatures was less than 1, meaning the exposure clearly exceeds what’s considered safe. In 2016, the World Health Organization’s cancer research agency classified “very hot beverages” above 65°C (149°F) as probably carcinogenic, regardless of what’s in them.
The practical takeaway: if you let your mate cool down before drinking, or drink it cold (as with tereré), this particular risk largely disappears. The same caution applies to very hot coffee or tea.
Caffeine Adds Up Fast
A single cup of yerba mate contains about 80 mg of caffeine, roughly equal to a cup of coffee. But here’s the catch: traditional preparation involves refilling the same gourd with hot water repeatedly throughout a sitting. This method can push total caffeine intake above 260 mg in a single session, the equivalent of about three cups of coffee.
That level of caffeine can cause insomnia, anxiety, rapid heartbeat, and digestive upset in sensitive individuals. It also creates dependency with regular use, leading to withdrawal headaches if you stop abruptly. For pregnant women, the March of Dimes recommends capping caffeine at 200 mg per day and specifically flags yerba mate as a source that’s hard to measure precisely. Their guidance is straightforward: pregnant women should avoid herbal caffeine sources like mate because the exact caffeine content is unpredictable.
It Can Block Iron Absorption
Yerba mate is rich in polyphenols, including quercetin, rutin, caffeic acid, and chlorogenic acid. These compounds act as antioxidants, which is often cited as a benefit, but they also bind to iron in your digestive tract. Specifically, they latch onto non-heme iron (the type found in plant foods, beans, and fortified grains) and form complexes your body can’t absorb.
For most people eating a varied diet, this isn’t a major issue. But if you’re already at risk for iron deficiency, whether from heavy periods, a plant-based diet, or a medical condition, drinking mate with meals could meaningfully reduce how much iron you absorb from food. Drinking it between meals rather than during them helps avoid this effect.
Rare but Real Liver Concerns
A case report published in Case Reports in Hepatology documented a 21-year-old man who developed acute hepatitis after drinking yerba mate daily for four months while living in Argentina. He presented with jaundice and severely elevated liver enzymes, with a biopsy showing a pattern of injury consistent with toxin or herbal supplement exposure. It was the first published case of liver damage attributed to yerba mate.
One case doesn’t mean the drink is broadly hepatotoxic. Millions of people consume it daily without liver problems. But it does suggest that in rare cases, possibly related to individual sensitivity or unusually high consumption, liver stress is possible. If you notice yellowing skin, dark urine, or unusual fatigue after starting regular yerba mate use, those are signs worth getting checked.
Medication Interactions
Because yerba mate contains caffeine, it interacts with the same medications that caffeine does. The most important interactions include:
- Blood thinners and anti-inflammatory drugs: Caffeine can reduce blood clotting, which may increase bruising or bleeding risk if you’re taking aspirin, warfarin, ibuprofen, naproxen, or heparin.
- Lithium: Caffeine increases how quickly your body clears lithium, so reducing or stopping mate consumption can cause lithium levels to spike unexpectedly.
- Diabetes medications: Caffeine can raise blood sugar after meals and reduce insulin sensitivity, potentially working against diabetes drugs.
- Sedatives: Mate can partially counteract benzodiazepines, sleep aids, and alcohol’s sedative effects.
- Clozapine and theophylline: Caffeine competes for the same liver enzymes that break down these drugs, causing their levels to build up in your bloodstream.
If you take any of these medications regularly, it’s worth factoring in your mate consumption the same way you would coffee.
Blood Sugar Effects for People With Diabetes
Yerba mate’s relationship with blood sugar is nuanced. A systematic review and meta-analysis published in Frontiers in Endocrinology found that mate consumption lowered post-meal blood sugar by about 13 mg/dL in people with pre-diabetes and modestly reduced long-term blood sugar markers. That sounds beneficial, and for some people it may be. But the researchers noted that these effects are likely driven by the stimulant properties of caffeine rather than anything unique to mate.
The concern for people on diabetes medication is that this blood sugar-lowering effect can stack with their drugs, increasing the risk of blood sugar dropping too low. Meanwhile, caffeine’s tendency to reduce insulin sensitivity can make blood sugar control less predictable overall. For people managing diabetes with medication, the combination creates an unpredictable push-and-pull on glucose levels that’s worth monitoring.
Smoke-Dried vs. Air-Dried Matters
Traditional yerba mate processing involves a step called sapeco, where fresh leaves are exposed to open flame and then smoke-dried. This is what introduces PAHs into the final product. Studies show that most of the PAH content in dried mate comes from this processing step, not from the plant itself, with fresh leaves containing substantially lower levels.
Air-dried or unsmoked yerba mate contains roughly a third of the PAH levels found in traditionally smoked versions. If you’re a daily drinker looking to reduce your overall exposure, seeking out brands that use air-drying or non-smoke methods is a simple way to lower one variable. Some brands now market specifically as “unsmoked,” though they’re less common than traditional varieties.