Several popular supplements can change the way your body smells, sometimes dramatically. Choline, L-carnitine, DHEA, garlic extracts, fenugreek, and high-dose fish oil are among the most common culprits. The mechanisms vary: some flood a metabolic pathway that produces trimethylamine (a compound that smells like rotting fish), others push sulfur-containing volatiles out through your skin, and at least one ramps up the hormonal activity of your sweat glands. Whether you actually develop noticeable odor depends on dose, your individual enzyme capacity, and the bacteria living on and inside you.
Choline and the Fishy Smell
Choline is an essential nutrient found in eggs, liver, and many multivitamins and nootropic stacks. Your gut bacteria convert some of the choline you eat into trimethylamine, or TMA, a small molecule with an unmistakable rotting-fish smell. Normally, an enzyme in your liver called FMO3 quickly converts TMA into an odorless compound that leaves through your urine. Problems arise when the amount of TMA produced exceeds what FMO3 can handle. High-dose choline supplements, especially those delivering 1,000 mg or more per day, can saturate this pathway and allow unmetabolized TMA to escape through sweat, breath, and urine.
The most severe version of this is a genetic condition called trimethylaminuria (sometimes called “fish odor syndrome”), in which FMO3 itself is deficient or absent. People with this condition produce a persistent fishy smell even from normal dietary choline intake.1PubMed Central. A review of trimethylaminuria: (fish odor syndrome) But you do not need the full genetic condition to experience the problem. Many people carry partial FMO3 variants that reduce enzyme activity without eliminating it. For these individuals, a choline supplement can tip the balance from manageable TMA load to noticeable odor. If you have started a choline supplement and notice a fishy smell on your skin or in your urine, the supplement is the likely explanation.
L-Carnitine and the Same Bottleneck
L-carnitine, widely sold for fat metabolism and exercise performance, feeds into the same TMA pathway as choline. Gut bacteria can convert carnitine into TMA just as they do with choline, and the same liver enzyme (FMO3) is responsible for neutralizing it. When carnitine intake from supplements pushes TMA production past the enzyme’s capacity, the excess TMA escapes through the same routes and produces the same fishy odor.
A clinical case report documented exactly this scenario: a patient developed fish odor syndrome during L-carnitine (levocarnitine) treatment, and the smell resolved after the supplement was stopped. The authors linked the effect to excess carnitine intake saturating the elimination pathway, particularly in situations where enzymatic metabolism was already somewhat limited.2PubMed Central. L-carnitine treatment and fish odor syndrome: an unwaited adverse effect This means the odor issue with L-carnitine is dose-dependent: a low dose may cause no problems, while a high dose, especially combined with a choline-rich diet, can overwhelm the system. If you are stacking both choline and carnitine supplements, you are loading the same bottleneck from two directions.
DHEA and Stronger-Smelling Sweat
DHEA (dehydroepiandrosterone) is a hormone precursor sold over the counter for anti-aging, energy, and libido support. Unlike choline and carnitine, DHEA does not produce odor through gut bacteria or liver enzymes. Instead, it acts on your sweat glands directly. DHEA is converted in the body into androgens, which stimulate apocrine sweat glands concentrated in the armpits and groin. Apocrine sweat itself is initially odorless, but it is rich in proteins and lipids that skin bacteria feed on enthusiastically, producing the compounds we recognize as body odor.
In a nine-month randomized clinical trial of DHEA replacement in patients with adrenal failure, 89 percent of participants receiving DHEA reported increased sweat odor as a side effect.3The Journal of Clinical Endocrinology & Metabolism. Replacement of Dehydroepiandrosterone in Adrenal Failure: No Benefit for Subjective Health Status and Sexuality in a 9-Month, Randomized, Parallel Group Clinical Trial That is a strikingly high rate. The change is not subtle: DHEA essentially turns up the volume on your apocrine glands, giving bacteria more raw material to work with. Standard deodorant and antiperspirant may not fully mask it, because the sweat composition itself has changed. If you have recently started DHEA and notice that your usual hygiene routine is no longer sufficient, the supplement is probably the reason.
Garlic Supplements and Sulfur Through the Skin
Garlic supplements deliver concentrated doses of organosulfur compounds, the same chemicals responsible for garlic’s pungent smell in the kitchen. When you ingest garlic, your body metabolizes its sulfur compounds into molecules like diallyl disulfide (DADS) and allyl methyl sulfide (AMS), and these are released not just through your breath but also through your skin. Researchers have directly measured these sulfur volatiles emanating from human skin after garlic ingestion. The emission of DADS spiked immediately after eating grilled garlic and tapered off over time, while AMS peaked about 30 minutes later and lingered, suggesting it accumulates in skin tissue before slowly diffusing out.4PubMed Central. Measurement of diallyl disulfide and allyl methyl sulfide emanating from human skin surface and influence of ingestion of grilled garlic
This means the garlic smell is not just on your breath; it is literally coming from your entire body surface. Concentrated garlic supplements, particularly aged garlic extract and allicin capsules, can produce the same effect. Odorless garlic supplements do exist and are marketed specifically to avoid this problem, though how effective they are at eliminating skin emissions varies by formulation. If garlic-related body odor bothers you but you want the cardiovascular or immune benefits, switching to an enteric-coated or deodorized formulation may help, but it is not guaranteed to eliminate the smell entirely, because some of the metabolic byproducts are generated internally regardless of how the supplement is coated.
Fenugreek and the Maple Syrup Smell
Fenugreek is popular in testosterone-boosting and lactation-support supplements. It contains a compound called sotolon, which has a distinctive sweet smell often described as maple syrup or caramel. Sotolon is excreted through sweat and urine, and at sufficient doses, fenugreek can make your body smell noticeably sweet. This effect has been documented in the medical literature since at least 1981, when clinicians reported that fenugreek ingestion caused a maple-syrup odor in urine that could be confused with maple syrup urine disease, a serious metabolic disorder.5PubMed. Maple-syrup urine odor due to fenugreek ingestion
The odor itself is not harmful, but it can be alarming if you do not know the cause. A sweet or burnt-sugar smell in urine or sweat can prompt unnecessary medical investigation if neither you nor your doctor connects it to fenugreek. The effect is dose-dependent and typically resolves within a day or two of stopping the supplement. Fenugreek odor is unusual among supplement-related smells because many people find it pleasant or at least neutral, unlike the fishy smell from choline or carnitine. Still, it can be strong enough that others notice it on your skin and clothing.
Fish Oil and Fishy Odor
Fish oil is one of the most commonly reported supplements for causing an unpleasant smell, mostly as fishy burps and a lingering aftertaste. The mechanism is simpler than with choline or carnitine: fish oil capsules contain omega-3 fatty acids derived from fish, and if the oil oxidizes (goes rancid) or if the capsule dissolves in the stomach rather than the intestine, you may literally taste and smell fish. Some of the volatile breakdown products of fish oil are the same compounds responsible for the smell of actual fish.
Whether fish oil contributes to body odor through the skin is less clear. A study examining breath ethane (a marker of fat oxidation in the body) found that ethane levels correlated with systemic lipid peroxidation but did not correlate with omega-3 fatty acid concentrations in the blood.6Metabolites / MDPI. Breath ethane concentrations in healthy volunteers correlate with a systemic marker of lipid peroxidation but not with omega-3 Fatty Acid availability In other words, having more omega-3s circulating does not automatically mean more oxidative byproducts being exhaled. The fish oil smell problem is likely more about the supplement itself (its quality, freshness, and coating) than about what happens after the fatty acids enter your bloodstream. Choosing a high-quality, molecularly distilled fish oil and storing it in the refrigerator tends to reduce the issue considerably. Enteric-coated capsules that dissolve in the intestine rather than the stomach also help with the fishy burp problem.
Why Some People React and Others Don’t
You may have noticed a pattern: much of supplement-related body odor comes down to enzyme capacity and bacterial populations. For the TMA pathway (choline, carnitine, and related compounds), variation in FMO3 enzyme activity is the main genetic factor. Full deficiency is rare, but partial variants are surprisingly common. People with reduced FMO3 activity may tolerate moderate dietary choline just fine but tip over into noticeable odor when a supplement adds to the load.1PubMed Central. A review of trimethylaminuria: (fish odor syndrome)
Your gut microbiome also plays a major role. The bacteria in your intestines are the ones converting choline and carnitine into TMA in the first place. Different people harbor different bacterial communities, and some produce far more TMA from the same dietary input than others. Similarly, the bacteria on your skin are responsible for converting the odorless components of apocrine sweat into smelly byproducts, which is why DHEA can cause dramatic odor changes in some people and milder ones in others. Researchers have noted that the accumulation of odorous compounds can result from diet, the specific composition of gut microbiota, and the functional capacity of the liver and kidneys.7PubMed Central. Microbiota and Malodor-Etiology and Management This means two people taking the same supplement at the same dose can have very different odor outcomes. Your particular combination of genetics, gut bacteria, liver function, and skin flora determines your personal threshold.
Hormonal status matters too. Women often report that supplement-related body odor fluctuates with their menstrual cycle, and menopause can change the picture again because FMO3 activity appears to be influenced by sex hormones. Liver and kidney health affect how efficiently your body clears odorous metabolites. Even hydration plays a minor role: more concentrated urine and sweat carry a higher concentration of whatever volatile compounds your body is trying to excrete.
Practical Steps to Reduce Supplement-Related Odor
The most obvious fix is reducing the dose or stopping the supplement, but that is not always desirable, especially if the supplement is medically indicated. Several strategies can help without requiring you to give up the supplement entirely.
For TMA-related odor from choline or carnitine, riboflavin (vitamin B2) deserves attention. FMO3 is a flavin-dependent enzyme, meaning it needs riboflavin to function. In at least one clinical case, supplementing with 200 mg of riboflavin per day produced an immediate and sustained reduction in TMA output and noticeable improvement in odor, without any changes to diet or other supplements.8PubMed Central. Riboflavin-responsive trimethylaminuria in a patient with homocystinuria on betaine therapy The logic is straightforward: if FMO3 is underperforming partly because of insufficient riboflavin, giving it more of its required cofactor can boost its activity. This is not a guaranteed fix for everyone, but it is inexpensive and low-risk.
Activated charcoal and copper chlorophyllin (a derivative of chlorophyll) have both been studied specifically for trimethylaminuria. In a study of Japanese patients with the condition, activated charcoal at 1.5 grams per day for ten days normalized urinary TMA levels. Copper chlorophyllin at 180 mg per day for three weeks produced a similar effect, and the benefits appeared to last several weeks after stopping, longer than those of charcoal.9PubMed. Effects of the dietary supplements, activated charcoal and copper chlorophyllin, on urinary excretion of trimethylamine in Japanese trimethylaminuria patients These results come from people with a diagnosed enzyme deficiency, so the effects in someone with normal FMO3 who is simply overloading it with supplements would likely be even more pronounced. Chlorophyllin supplements (often sold as “chlorophyll capsules” or “internal deodorant”) are widely available and are one of the few supplements marketed specifically to reduce body odor from the inside out.
For garlic-related odor, the options are more limited because the sulfur compounds are an inherent part of how garlic works in the body. Switching to an aged garlic extract, which contains fewer of the most volatile sulfur compounds, can reduce the intensity. Taking garlic supplements with food may also slow absorption and reduce the sharp spike in skin emissions. For DHEA-related sweat odor, the main levers are standard ones: antibacterial soap targeted at the armpits, clinical-strength antiperspirant, and possibly probiotic-based deodorants designed to shift skin bacterial populations toward less odor-producing strains.
When Body Odor From a Supplement Signals Something Else
Occasionally, a new body odor that coincides with starting a supplement is not caused by the supplement at all. It is worth knowing when to look deeper. A persistent fishy smell that does not resolve after stopping choline or carnitine could indicate primary trimethylaminuria, the inherited FMO3 deficiency. This condition affects daily life significantly, and a urine test measuring the ratio of TMA to its oxidized form (TMAO) can confirm or rule it out.1PubMed Central. A review of trimethylaminuria: (fish odor syndrome) Liver and kidney problems can also impair the clearance of odorous metabolites, making supplement-related odor worse or creating new odor where none existed before.7PubMed Central. Microbiota and Malodor-Etiology and Management
A sweet or maple-syrup odor that persists after stopping fenugreek warrants a conversation with your doctor, because maple syrup urine disease (a rare but serious metabolic disorder) produces a similar smell. And a sudden, strong change in body odor unconnected to any new supplement could be a sign of an underlying metabolic issue, infection, or hormonal shift that deserves investigation on its own terms. The simplest diagnostic step is always to stop the suspected supplement for a week or two and see if the odor resolves. If it does, the supplement was the cause. If it does not, something else is going on.
Betaine, MSM, and Other Sulfur-Containing Supplements
Beyond the major offenders, a few other supplements deserve mention. Betaine (trimethylglycine), often taken for liver support or homocysteine management, is a direct source of methyl groups that gut bacteria can convert into TMA. It works through the same pathway as choline and carnitine, so the same fishy-odor risk applies. In fact, the riboflavin case study mentioned earlier involved a patient on betaine therapy who developed odor problems specifically because of the TMA load from betaine.8PubMed Central. Riboflavin-responsive trimethylaminuria in a patient with homocystinuria on betaine therapy
MSM (methylsulfonylmethane), a sulfur-containing supplement used for joint health and inflammation, can contribute sulfur compounds to sweat and breath in some users. The effect is typically mild compared to garlic supplements, but people who are sensitive to sulfur odors or who are already taking other sulfur-containing supplements may notice it. Similarly, N-acetyl cysteine (NAC), a popular antioxidant and liver-support supplement, is a sulfur amino acid derivative. Some users report a sulfurous smell in their urine or sweat, particularly at higher doses. These effects tend to be less dramatic than those from the major culprits listed above, but they can combine with each other. If you are taking a stack that includes multiple sulfur-containing or TMA-producing supplements, the additive effect on odor can be greater than what any single supplement would produce alone.
Dose management is usually the most effective strategy across all of these supplements. Body odor from supplements is almost always dose-dependent: there is some threshold below which your body’s clearance mechanisms keep up, and above which odorous metabolites start escaping. Finding that threshold for your particular body often means gradually reducing the dose until the odor disappears, then holding there. For choline specifically, spreading the dose across the day rather than taking it all at once can help, because it gives FMO3 more time to process each batch of TMA rather than being overwhelmed by a single surge.