Are nightshades bad for you?
The claim: Nightshades are poisonous and cause inflammation.
Last checked 8 October 2026
The poison part is real, mostly about potatoes, and EFSA's safety margin is tighter than most people expect. The inflammation part is unproven either way.
Potatoes carry glycoalkaloids that can make you ill, mostly from green, sprouting or damaged potatoes and the peel. EFSA saw symptoms start at 1 mg per kg of body weight in a day, and treats intake as no concern when it is more than 10 times below that. For a 70 kg adult that margin is used up by about 140 g of raw, unpeeled potato at a typical glycoalkaloid content; peeling and cooking lower the amount, by very different degrees. We found no randomized trial in people that has tested whether nightshades inflame joints or the gut.
Which foods are nightshades?
Nightshades are one plant family, Solanaceae. Here are the common foods in it, and some that people often think are in it, with the family Kew's Plants of the World Online gives for each:
| Food | Scientific name | Family | Nightshade? | Source |
|---|---|---|---|---|
| Potato | Solanum tuberosum | Nightshade family (Solanaceae) | Yes | Kew Plants of the World Online |
| Tomato | Solanum lycopersicum | Nightshade family (Solanaceae) | Yes | Kew Plants of the World Online |
| Eggplant (aubergine) | Solanum melongena | Nightshade family (Solanaceae) | Yes | Kew Plants of the World Online |
| Red bell pepper | Capsicum annuum | Nightshade family (Solanaceae) | Yes | Kew Plants of the World Online |
| Chili peppers | Capsicum annuum, Capsicum chinense, Capsicum frutescens | Solanaceae | Yes | Capsicum annuum, Capsicum chinense, Capsicum frutescens |
| Goji berry | Lycium barbarum | Solanaceae | Yes | Kew Plants of the World Online |
| Tomatillo | Physalis philadelphica | Solanaceae | Yes | Kew Plants of the World Online |
| Sweet potato | Ipomoea batatas | Morning glory family (Convolvulaceae) | No | Kew Plants of the World Online |
| Onion | Allium cepa | Amaryllis family, onion group (Amaryllidaceae) | No | Kew Plants of the World Online |
| White button mushrooms | Agaricus bisporus | Mushroom family (Agaricaceae); fungus, not a plant | No | Species Fungorum |
| Black pepper | Piper nigrum | Piperaceae | No | Kew Plants of the World Online |
Sweet potato, black pepper, onion and mushrooms are not nightshades.
The real poison: potato glycoalkaloids
Potatoes make glycoalkaloids (mainly solanine and chaconine) to fight off pests and germs. The European Food Safety Authority reviewed them in 2020:
In humans, acute toxic effects of potato GAs (α-solanine and α-chaconine) include gastrointestinal symptoms such as nausea, vomiting and diarrhoea.
the CONTAM Panel identified a lowest-observed-adverse-effect level of 1 mg total potato GAs/kg body weight (bw) per day as a reference point for the risk characterisation following acute exposure.
In humans, no evidence of health problems associated with repeated or long-term intake of GAs via potatoes has been identified.
No reference point for chronic exposure could be identified from the experimental animal studies.
The MOEs for the younger age groups indicate a health concern for the food consumption surveys with the highest mean exposure, as well as for the P95 exposure in all surveys. For adult age groups, the MOEs indicate a health concern only for the food consumption surveys with the highest P95 exposures.
an MOE higher than 10 indicates that there is no health concern.
MOE is the margin of exposure: how many times below the 1 mg level an intake sits. So EFSA wants intake more than 10 times below the level that made people ill. Its concern is for young children and the heaviest potato eaters, not for most people.
What a real potato carries
Using EFSA's own figures for potatoes as sold (raw, with skin), for a 70 kg adult:
| Potato | Glycoalkaloids per 100 g | In one medium raw potato (213 g) | Margin of exposure (70 kg adult) | Raw potato that uses up EFSA's margin of 10 | Raw potato that reaches EFSA's level (70 mg) |
|---|---|---|---|---|---|
| Typical potato (EFSA mean) | 5.12 mg | 10.9 mg | 6.4 | 140 g | 1400 g |
| High-end potato (EFSA P95: 95% of potatoes tested had less) | 11.7 mg | 24.9 mg | 2.8 | 60 g | 600 g |
Peeling and cooking lower these figures, by very different amounts (see below). Germany's Federal Institute for Risk Assessment (BfR) uses a different reference point, a no-effect level, and adds a limit for the potatoes themselves. It calls both provisional:
The Federal Institute for Risk Assessment (BfR) has derived a NOAEL (No Observed Adverse Effect Level – the highest dose at which no undesired health effects were observed) of 0.5 mg per kg body weight and day.
the BfR recommends that the glycoalkaloid content of potatoes intended for consumption should lie below 100 mg per kg fresh weight.
In view of the current incomplete data, these recommendations should be regarded as provisional.
Green, sprouting and bitter potatoes
Most of the risk sits in potatoes that have been mishandled:
The presence of green parts indicates an elevated glycoalkaloid content.
The consumption of green, sprouting or damaged potatoes can lead to poisoning through glycoalkaloids.
Deaths as a result of glycoalkaloid poisoning have not been reported in the last 50 years.
There are also reports of isolated instances of deadly poisoning.
the peeling of potatoes reduced the GA content by 25–75%, boiling in water and blanching of peeled potatoes by 5–65% and frying in oil of peeled potatoes by 20–90%.
The BfR's own advice includes: "Small children in particular should only eat peeled potatoes" and "Potato dishes should not be eaten if they have a bitter taste".
Tomatoes, eggplant and peppers
Tomatoes and eggplant make their own glycoalkaloids, not solanine. Ripeness makes a big difference:
low-tomatine red tomatoes (0.03-0.08 mg/100 g), intermediate-tomatine tomatoes (0.1-0.8 mg/100 g), and high-tomatine fresh and processed green, including pickled and fried, tomatoes (0.9-55 mg/100 g).
there is no evidence to consider α-tomatine as a substance of concern and there are no reports of acute toxicity in humans due to ingestion of green tomatoes.
In the commercially unripe and ripe stages, the TGA content was relatively low (mean content: 125 and 230 mg/kg dry weight (dw), respectively), while in the commercially overripe stage, a strong increase of the TGA content (mean 1,937 mg/kg dw) was observed.
For tomato and aubergine GAs, the risk to human health could not be characterised due to the lack of occurrence data and the limited toxicity data.
The third quote is eggplant (aubergine): its glycoalkaloids climb steeply once the fruit is overripe. EFSA could not characterise the risk from tomato or eggplant glycoalkaloids, so this site shows their amounts without a limit.
Do nightshades cause inflammation?
This is the claim most people mean. A fair summary comes from the Arthritis Foundation:
There’s little scientific evidence on either side, but a lot to be said for lived experience.
Despite patient reports, there is a lack of randomized controlled trials (RCTs) investigating the effects of nightshades on patients with RA.
That second quote is from the plan for a trial in people with rheumatoid arthritis (RA), published in 2024; we found no published results yet. The animal studies point both ways. EFSA describes mice bred to develop gut inflammation:
This treatment aggravated intestinal injury, as determined by pathohistological diagnosis, while in control animals no effect could be seen.
Disruption of epithelial barrier integrity by GAs may be important in triggering inflammatory bowel disease in susceptible individuals.
Plant extracts of S. tuberosum as well as GA and aglycones exerted pronounced anti-inflammatory effects in in vitro and in vivo experiments
S. tuberosum is the potato. So potato glycoalkaloids made gut injury worse in mice already prone to it, while potato extracts calmed inflammation in other cell and animal tests. Neither tells us what a normal serving does to a person.
What you'll hear at the table
The same arguments come up whenever nightshades are argued over. Here is each one, checked against its source.
You'll hear: Nightshades cause inflammation and make arthritis worse.
Not settled
Many people say so, and we found no randomized trial in people that has tested it (see "Do nightshades cause inflammation?" above). The animal studies point both ways.
When evaluating these studies, it’s important to keep in mind that mouse studies rarely translate well to human beings.
You'll hear: Potatoes are poisonous.
Partly holds up
Potatoes do carry a real toxin, and it has made people ill. EFSA found a health concern for some young children and for the heaviest potato eaters, not for most people (see "The real poison" above).
The highest number of survey days with intake of potatoes below the MOE of 10 was estimated for toddlers (56%) followed by children (50%). For the other age groups, the estimated TGA intake was below the MOE of 10 in up to 22–40% of the survey days.
Only a few cases of poisoning caused by the consumption of potato dishes have been reported and documented in the last 100 years.
Due to the non-specific symptoms, however, the actual number could be considerably higher.
Those are the worst surveys EFSA looked at, counting only days when potatoes were eaten. TGA means total glycoalkaloids.
You'll hear: Green potatoes can poison you.
Holds up
The consumption of green, sprouting or damaged potatoes can lead to poisoning through glycoalkaloids.
Green parts and so-called “eyes” should be generously removed from potatoes
Increases of solanine in the potato peel are closely associated with greening (synthesis of chlorophyll) of the peel. These biochemical processes are independent of each other, but are both activated by light.
So the green is a warning sign: light drives both the green and the glycoalkaloids.
You'll hear: Cooking gets rid of solanine.
Partly holds up
Cooking and peeling both lower it, by very different amounts. The compounds themselves survive high heat:
GAs as pure standards are stable to temperatures up to 150°C
the peeling of potatoes reduced the GA content by 25–75%, boiling in water and blanching of peeled potatoes by 5–65% and frying in oil of peeled potatoes by 20–90%.
Consumers should not reuse the water in which potatoes have been boiled as some of the glycoalkaloids can pass over to the cooking water
You'll hear: All nightshades contain solanine.
Doesn't hold up
Solanine is the potato's main glycoalkaloid. EFSA names a different pair for each of the three nightshades it assessed:
potato (α-solanine and α-chaconine), aubergine (α-solasonine and α-solamargine) and tomato (α-tomatine and α-dehydrotomatine)
You'll hear: Green tomatoes are poisonous.
Doesn't hold up
Green tomatoes carry far more tomatine than red ones, but no one has been reported poisoned by them. EFSA also says it had little data to judge tomato glycoalkaloids (see above):
high-tomatine fresh and processed green, including pickled and fried, tomatoes (0.9-55 mg/100 g)
there are no reports of acute toxicity in humans due to ingestion of green tomatoes.
You'll hear: Nightshades contain nicotine.
Partly holds up
Some do, in traces measured in billionths of a gram (ng). Black tea, which isn't a nightshade, can carry more:
The average values for nicotine in tomato and potato were 7.3 ng/g wet weight and 15 ng/g wet weight, respectively.
Black teas, including regular and decaffeinated brands, had nicotine contents ranging from non-detectable to greater than 100 ng/g wet weight.
Nicotine was not detected (less than 1 ng/ml of extract) in egg plant or green pepper.
You'll hear: Sweet potatoes are nightshades.
Doesn't hold up
Sweet potato is in the morning glory family (Convolvulaceae), not the nightshade family, despite the name (see the family table above).
You'll hear: Black pepper is a nightshade.
Doesn't hold up
Black pepper is in a different family (Piperaceae). Chili peppers are nightshades; black pepper is not (see the family table above).
You'll hear: Cutting out nightshades clears up psoriasis.
Not settled
In a US survey of people with psoriasis, about half of those who had cut nightshades said their skin improved. Many said the same after adding vegetables:
The percentage of patients reporting skin improvement was greatest after reducing alcohol (53.8%), gluten (53.4%), nightshades (52.1%), and after adding fish oil/omega-3 (44.6%), vegetables (42.5%), and oral vitamin D (41%).
Self-reported, by people who chose to answer. It is a reason to test the idea, not proof.
The referee's verdict
- Right, for the "avoid them" side: potato glycoalkaloids are real toxins; green, sprouting and bitter potatoes can make you ill; EFSA's margin of 10 is used up by a fairly small amount of raw, unpeeled potato, and EFSA sees a health concern for young children and the heaviest potato eaters; and many people say they feel better without nightshades.
- Right, for the "eat them" side: a normal portion of a normal potato is below the level where EFSA saw symptoms start; no long-term harm from potatoes has been found in people; EFSA found no evidence that tomatine is a substance of concern; and the nicotine is a trace.
- Not known: whether nightshades worsen arthritis, gut inflammation or psoriasis in people. We found no randomized trial that has measured it.
Try it with your own plate
Put potatoes on the plate builder to see the glycoalkaloids in your own portion against EFSA's level, at your own body weight.
Sources
- EFSA Panel on Contaminants in the Food Chain (2020). Risk assessment of glycoalkaloids in feed and food, in particular in potatoes and potato-derived products. EFSA Journal 18(8): e06222. doi:10.2903/j.efsa.2020.6222Evidence: Regulatory assessmentRead: Wiley full text, in Chrome
- German Federal Institute for Risk Assessment (BfR). Frequently asked questions about solanine (glycoalkaloids) in potatoes. FAQ of 23 April 2018 (English translation).Evidence: Regulatory assessmentRead: PDF text layer, in Chrome
- Friedman M, Levin CE (1995). alpha-Tomatine content in tomato and tomato products determined by HPLC with pulsed amperometric detection. Journal of Agricultural and Food Chemistry 43: 1507–1511.Evidence: Measured in foodRead: abstract on FAO AGRIS, in Chrome
- Davis RA, Stiles MF, deBethizy JD, Reynolds JH (1991). Dietary nicotine: a source of urinary cotinine. Food and Chemical Toxicology 29(12): 821–827.Evidence: Measured in foodRead: PubMed abstract, in Chrome
- Arthritis Foundation. What You Should Know About Nightshades and Arthritis.Evidence: Not applicable. A US patient charity's summary of the evidence.Read: page text, in Chrome
- Golmohammadi A, Hosseinikia M, Sadeghi MK, Golampur D, Hosseinzadeh Z, Panahande SB (2024). The evaluation of nightshade elimination diet (NED) on inflammatory and rheumatologic markers of rheumatoid arthritis patients: study protocol for a randomized controlled trial. Trials 25. doi:10.1186/s13063-024-08372-7Evidence: Not applicable. A trial plan (protocol), not results.Read: article text, in Chrome
- Afifi L, Danesh MJ, Lee KM, Beroukhim K, et al. (2017). Dietary Behaviors in Psoriasis: Patient-Reported Outcomes from a U.S. National Survey. Dermatology and Therapy 7(2): 227–242. doi:10.1007/s13555-017-0183-4Evidence: Human observational study. Self-reported survey of 1,206 people with psoriasis.Read: PMC full text, in Chrome
- Royal Botanic Gardens, Kew. Plants of the World Online.Evidence: Not applicable. The botanical name and family reference used for every ID card on this site.Read: POWO API and taxon records, in Chrome