Chlorophyll supplements have become increasingly popular, marketed with claims about detoxification, cancer prevention, weight loss and body odour control. Walk through any health food shop and you’ll find liquid chlorophyll, chlorophyll tablets and chlorophyll drops, often with impressive-sounding health claims on the packaging.

But what does the clinical research actually show? I’ve gone through the published studies to separate the evidence-based benefits from the marketing hype.

What is chlorophyll?

Chlorophyll is the green pigment found in plants and algae that absorbs sunlight for photosynthesis. It’s what makes leaves green and enables plants to convert carbon dioxide and water into food using solar energy.

The molecular structure of chlorophyll resembles haem, the iron-containing compound in haemoglobin that carries oxygen in your blood. The key difference is that chlorophyll has a magnesium atom at its centre rather than iron. This structural similarity has led to speculation about potential health benefits, though the evidence for most claims remains limited.

Chlorophyll is fat-soluble, which means it doesn’t dissolve well in water and can be unstable when extracted from plants. This creates problems for supplement manufacturers, which is why most chlorophyll supplements don’t actually contain chlorophyll at all.

Chlorophyll versus chlorophyllin: an important distinction

Here’s something most supplement companies don’t advertise prominently: the “chlorophyll” supplements you buy over the counter typically contain chlorophyllin, not natural chlorophyll.

Chlorophyllin is a semi-synthetic derivative made by treating chlorophyll (usually extracted from alfalfa or fescue grass) with sodium and copper salts. The resulting compound, sodium copper chlorophyllin, is water-soluble, more stable than natural chlorophyll, and significantly cheaper to produce.

Whether chlorophyllin has the same biological effects as natural chlorophyll is an open question. Most research has used chlorophyllin rather than chlorophyll, so when I discuss the evidence below, keep in mind that these findings may not apply to natural chlorophyll from food sources like spirulina or leafy green vegetables.

Benefits supported by clinical evidence

1. Chlorophyll may help with seasonal allergic rhinitis

Allergic rhinitis affects roughly 10-30% of adults worldwide, causing symptoms like runny nose, nasal congestion, sneezing and itchy nose. It’s triggered by allergens such as pollen, dust mites, pet dander and mould.

A randomised, double-blind, placebo-controlled trial published in 2016 tested oral chlorophyll capsules in 66 patients with seasonal allergic rhinitis over 12 weeks. The daily dose was remarkably small (0.7 mg), yet the chlorophyll group showed reduced need for rescue allergy medications compared to placebo, as measured by rescue medication scores [1].

My take: This is interesting but far from conclusive. The sample size was small (66 patients) and I’m not aware of any replication studies. The mechanism by which such a tiny dose would affect allergy symptoms isn’t clear. I wouldn’t recommend chlorophyll as a primary treatment for hay fever, but it might be worth trying as an adjunct if conventional treatments aren’t fully controlling your symptoms.

2. Chlorophyll may reduce aflatoxin-associated liver cancer risk

This is probably the most robust finding in chlorophyll research, though it applies to a very specific situation.

Aflatoxin B1 is a potent carcinogen produced by certain moulds that can contaminate crops like peanuts, corn, tree nuts and grains. It’s a significant problem in parts of Africa and Asia where food storage conditions allow mould growth. Chronic aflatoxin exposure is strongly linked to liver cancer, particularly in people with hepatitis B infection.

When aflatoxin is metabolised in the body, it produces AFB1-N7-guanine, a DNA adduct (a compound that binds to DNA) that can be measured in urine as a marker of aflatoxin exposure and DNA damage.

A randomised, double-blind, placebo-controlled trial in China studied 180 healthy adults living in a region with high aflatoxin exposure. After four months of daily chlorophyllin supplementation, urinary AFB1-N7-guanine levels were 55% lower in the chlorophyllin group compared to placebo [2].

This doesn’t prove that chlorophyllin prevents liver cancer, but reducing a known carcinogenic biomarker by 55% is meaningful. The proposed mechanism is that chlorophyllin binds to aflatoxin in the gut, reducing its absorption.

Who cares about this finding? If you live in a developed country with good food safety standards, probably not you. Aflatoxin contamination is heavily regulated in the UK, US and EU. But for people in high-risk regions, chlorophyllin supplementation could be a simple, cheap intervention worth considering.

3. Chlorophyll may help control body odour

Body odour results from bacteria breaking down sweat and other secretions on the skin. While usually just a social nuisance, excessive or unusual body odour can cause significant distress.

An older study from the 1980s looked at 62 elderly nursing home residents taking oral chlorophyllin. The researchers reported improvements in body odour and faecal odour, along with reduced constipation and flatulence [3]. However, this wasn’t a controlled trial, so the findings should be interpreted cautiously.

More convincingly, chlorophyll has been studied in trimethylaminuria, a rare metabolic disorder where the body cannot break down trimethylamine, a compound that smells like rotting fish. People with this condition have a persistent fishy odour in their sweat, urine and breath. A study found that oral chlorophyllin significantly reduced urinary trimethylamine concentrations in affected patients [4].

My honest assessment: The evidence for general body odour control is weak (one uncontrolled study in elderly nursing home residents isn’t compelling). But for the specific condition of trimethylaminuria, chlorophyllin appears genuinely helpful. If you have this rare disorder, it’s worth discussing chlorophyll supplementation with your doctor.

4. Chlorophyll combined with phototherapy may improve acne

Acne vulgaris affects the majority of teenagers and can persist into adulthood. While not dangerous, severe acne causes scarring and psychological distress.

Photodynamic therapy uses light to activate a photosensitising compound applied to the skin, generating reactive oxygen species that kill bacteria and reduce sebum production. A controlled study compared standard phototherapy alone versus phototherapy combined with a topical chlorophyllin-liposomal complex in 24 acne patients over four weeks [5].

The combination therapy group showed significantly greater reductions in acne lesions, severity scores and sebum levels compared to phototherapy alone.

The catch: This was a small study (24 patients), and the chlorophyll was applied topically in combination with light therapy rather than taken orally. You can’t extrapolate from this to oral chlorophyll supplements or topical chlorophyll used without phototherapy. This is a specialised dermatological treatment, not something you can replicate at home with liquid chlorophyll drops.

5. Dietary chlorophyll may be associated with lower colorectal cancer risk

Red and processed meat consumption is associated with increased colorectal cancer risk. One proposed mechanism involves haem iron from meat promoting the formation of potentially carcinogenic compounds in the gut.

A large population study (the Netherlands Cohort Study) followed over 120,000 participants for 9.3 years. Researchers found that higher chlorophyll intake was associated with lower colorectal cancer risk in men, particularly among those with high haem iron intake [6].

The theory is that chlorophyll may bind to haem iron metabolites in the gut, similar to how it binds aflatoxin, preventing harmful compounds from damaging the intestinal lining.

Important caveat: This is observational data, not a clinical trial. People who eat more chlorophyll (from leafy greens and other vegetables) likely have healthier diets overall, which could explain the association. We can’t conclude that chlorophyll supplements would have the same protective effect.

Side effects of chlorophyll

Oral chlorophyll and chlorophyllin are generally well tolerated. The most commonly reported side effects are mild gastrointestinal symptoms:

Diarrhoea
Nausea
Vomiting (rare)

Perhaps the most noticeable “side effect” isn’t really a side effect at all: chlorophyll can turn your urine green and your stool dark green or black. This is harmless and simply reflects the pigment passing through your digestive system, but it can be alarming if you’re not expecting it.

Safety precautions (6 contraindications)

While chlorophyll supplements are considered safe for most adults, there are situations where caution is warranted.

1. Topical application may cause skin irritation. When applied to wounds or skin, chlorophyllin can cause burning or itching sensations.

2. Pregnancy, breastfeeding and children. The safety of chlorophyll supplements during pregnancy and lactation hasn’t been established. If you’re pregnant or breastfeeding, or considering chlorophyll for a child, it’s best to stick with food sources of chlorophyll (green vegetables) rather than supplements.

3. Liver or kidney disease. How chlorophyll is metabolised and excreted in people with impaired organ function isn’t well studied. If you have significant liver or kidney problems, consult your doctor before supplementing.

4. Interference with faecal occult blood tests. The green/black discolouration of stool caused by chlorophyll can interfere with faecal occult blood tests used to screen for colorectal cancer. Stop chlorophyll supplementation at least a week before any planned stool testing.

5. Allergic reactions. Though rare, allergic reactions to chlorophyll can occur. Symptoms include rash, swelling of the face, lips, tongue or throat, and difficulty breathing. People with known allergies to plants, fruits, vegetables or nuts may be at higher risk. Discontinue use immediately if you experience any allergic symptoms.

6. Photosensitivity and drug interactions. Chlorophyll may increase skin sensitivity to sunlight. This becomes particularly concerning if you’re taking other medications that also cause photosensitivity. Taking both together could increase your risk of sunburn, blistering or skin damage when exposed to UV light.

Medications that can cause photosensitivity include:

NSAIDs: ibuprofen, diclofenac, naproxen
Diuretics: furosemide, hydrochlorothiazide
Antibiotics: ciprofloxacin, norfloxacin, levofloxacin, tetracycline
Tricyclic antidepressants: amitriptyline
Antifungals: itraconazole, griseofulvin
Retinoids: isotretinoin, acitretin
Sulphonamides: trimethoprim-sulfamethoxazole
Diabetes medications: glipizide, glyburide
Statins: atorvastatin, fluvastatin
Psoriasis medications: methoxsalen, trioxsalen

If you’re taking any of these medications, either avoid chlorophyll supplements or be extremely diligent about sun protection (high-SPF sunscreen, protective clothing, avoiding peak UV hours).

The bottom line

Chlorophyll supplements have some evidence supporting specific uses, particularly reducing aflatoxin absorption in high-risk populations and managing trimethylaminuria. The evidence for allergic rhinitis is preliminary but intriguing. Claims about general detoxification, weight loss, energy boosting and anti-ageing are not supported by clinical research.

For most people, eating plenty of green vegetables will provide chlorophyll along with fibre, vitamins, minerals and other beneficial compounds. The added benefit of chlorophyll supplements over a vegetable-rich diet is uncertain.

If you do choose to supplement, be aware of the potential for photosensitivity, the harmless but sometimes alarming colour changes to urine and stool, and the need to stop before faecal occult blood testing.

References

Mao W, Xiang W, Zheng S. Effects of chlorophyll on patients with seasonal allergic rhinitis: a pilot study. Journal of Medicinal Food. 2016;19(9):873-878. PMID: 27277115
Egner PA, Wang JB, Zhu YR, et al. Chlorophyllin intervention reduces aflatoxin-DNA adducts in individuals at high risk for liver cancer. Proceedings of the National Academy of Sciences USA. 2001;98(25):14601-14606. PMCID: PMC64728
Young RW, Beregi JS Jr. Use of chlorophyllin in the care of geriatric patients. Journal of the American Geriatrics Society. 1980;28(1):46-47. PMID: 7350215
Yamazaki H, Fujieda M, Togashi M, et al. Effects of the dietary supplements, activated charcoal and copper chlorophyllin, on urinary excretion of trimethylamine in Japanese trimethylaminuria patients. Life Sciences. 2004;74(22):2739-2747. PMID: 15043988
Zheng W, Wu Y, Winter P, et al. Exploratory investigation of chlorophyllin with photodynamic therapy for acne vulgaris. Dermatology. 2014;229(2):102-110. PMID: 24930587
Balder HF, Vogel J, Jansen MC, et al. Heme and chlorophyll intake and risk of colorectal cancer in the Netherlands cohort study. Cancer Epidemiology, Biomarkers & Prevention. 2006;15(4):717-725. PMID: 16614114
NHS. Complementary and alternative medicine. Available at: https://www.nhs.uk/conditions/complementary-and-alternative-medicine/
Mount Sinai Health Library. Chlorophyll. Available at: https://www.mountsinai.org/health-library/supplement/chlorophyll