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Tongkat Ali · Eurycoma longifolia
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In one pass Tongkat ali is the root of a tree from the Southeast Asian rainforest. Not this — Tongkat Ali strongly raises testosterone — Testosterone rises about 10%, on the same order as ashwagandha — within normal physiological variation and far below what the marketing claims.
Educational content, not medical advice — consult a clinician.
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Chapter 1
A Southeast Asian tree root
Tongkat ali is the root of a tree from the Southeast Asian rainforest. It is intensely bitter, and local people have long boiled it into a tea. In recent years fitness circles and podcasts have promoted it as a natural testosterone booster: no injections and no prescription drugs, just a root that is supposed to push up testosterone (the main male sex hormone).
The compounds thought to do the work are a class of bitter substances called quassinoids. The lead one is eurycomanone, the name extract makers print on the label with its content. In cell and animal experiments, it holds back the step that turns testosterone into estrogen while nudging the testosterone-making cells in the testes to work harder. Whether the same happens in people has not been shown directly (the chapter How it affects testosterone goes into detail).
The clearest signals in human studies appear in people whose testosterone was already low or who were under long-term stress, and most of those studies are small. The tree grows slowly, and good roots are scarce and valuable, so when you buy tongkat ali, the bigger worry is often what is actually in the bottle.
The compounds thought to do the work are a class of bitter substances called quassinoids. The lead one is eurycomanone, the name extract makers print on the label with its content. In cell and animal experiments, it holds back the step that turns testosterone into estrogen while nudging the testosterone-making cells in the testes to work harder. Whether the same happens in people has not been shown directly (the chapter How it affects testosterone goes into detail).
The clearest signals in human studies appear in people whose testosterone was already low or who were under long-term stress, and most of those studies are small. The tree grows slowly, and good roots are scarce and valuable, so when you buy tongkat ali, the bigger worry is often what is actually in the bottle.
Background · Where the tree grows and how it was used
Its botanical name is Eurycoma longifolia. It is native to Indonesia, Malaysia and Vietnam and also grows in Cambodia, Myanmar, Laos and Thailand. In Malay it is called Tongkat Ali (literally Ali's walking stick), in Indonesian Pasak Bumi, and English-language marketing likes to call it Malaysian ginseng. The part used as medicine is mainly the root, traditionally boiled into a tea.The tree grows slowly, and a wild root takes several years before it is considered ready for use. Because good roots are scarce and valuable, adulterated and substituted products are especially common.
Traditionally, people in Malaysia and Indonesia used the root for male vigor, against aging and fatigue, and for recovery after illness, as well as to bring down fever and as an aid against malaria; the bark was used against intestinal worms. What modern research actually picked up on was its old reputation as an aphrodisiac.
In practice · Black root, white root, standardized extract
Roots also come in grades. White root from young trees has the least of the active compounds and is cheapest; black root from old trees has the most and is most expensive. Cheap products often mix in white root or roots of other plants and sell them as black root, so the name on the bottle is not enough.The extracts used most often in trials, and the most reliable, are a few standardized extracts (Physta®, LJ100® and similar), which at least state their eurycomanone content. With an unstandardized root powder, you do not know what is actually inside.
Chapter 2
How it affects testosterone
Tongkat ali may affect testosterone along two routes, and only people who start low have room to go up.
The first is pushing production. Making testosterone is an assembly line: the brain sends a signal to the interstitial cells of the testes (Leydig cells), which turn cholesterol into testosterone step by step. In cell and animal experiments, eurycomanone loosens the slow first step on this line and holds back the step that turns testosterone into estrogen. Whether this happens in people has not been measured directly.
The second is releasing the brake. Under long-term stress, the stress hormone cortisol stays high and presses down on the same line. In a trial of 63 moderately stressed adults, salivary cortisol fell 16% after 4 weeks. Ease that brake and some testosterone may come back on its own: no testosterone is added; a brake is lifted.
So who it might help depends on which route still has room in your body.
The first is pushing production. Making testosterone is an assembly line: the brain sends a signal to the interstitial cells of the testes (Leydig cells), which turn cholesterol into testosterone step by step. In cell and animal experiments, eurycomanone loosens the slow first step on this line and holds back the step that turns testosterone into estrogen. Whether this happens in people has not been measured directly.
The second is releasing the brake. Under long-term stress, the stress hormone cortisol stays high and presses down on the same line. In a trial of 63 moderately stressed adults, salivary cortisol fell 16% after 4 weeks. Ease that brake and some testosterone may come back on its own: no testosterone is added; a brake is lifted.
So who it might help depends on which route still has room in your body.
Evidence · What each of three groups showed
Put the two routes together and you can see why there is a signal in some people and almost none in others:People under heavy stress: mainly route two. In Talbott 2013 salivary testosterone rose 37%, but saliva essentially measures the small free fraction, so this is not a 37% rise in serum total testosterone.Middle-aged and older men with low testosterone (hypogonadism): mainly route one. In the single-arm study Tambi 2012, the share of men with testosterone in the normal range went from 35.5% to 90.8% after 1 month. In the pooled analysis Leisegang 2022, the rise in total testosterone was confirmed in the hypogonadism subgroup.Healthy young adult men: their testosterone is already in the normal range, and the body's negative feedback (when testosterone is high, the brain sends less signal) pulls it back (textbook knowledge). The pooled analysis includes trials in healthy volunteers that also reported rises, but trials in this group are few and small.
You do not need to remember names on route one such as CYP17A1 (a key enzyme on the testosterone assembly line) or StAR (the protein that moves cholesterol into mitochondria). It is enough to know that, in experiments, eurycomanone loosens the steps that make testosterone.
Myth · It is not a stand-in for TRT
Let us state the limits clearly, so marketing does not lead you astray:It does not add testosterone to the body; it lets the body make a little more of its own.Still less is it a stand-in for (testosterone replacement therapy). TRT supplies testosterone directly from outside to bring a confirmed low level back into the normal range, under a doctor's monitoring. The changes seen with tongkat ali in trials are much smaller, and it has never been compared with TRT directly.Nor is it a boost for healthy young men: in people who are not low, the change you can see is small.
For reduced fatigue and better sperm quality there are some weaker signals (semen measures improved in a study of infertile men that had no control group). Claims that it slows aging, burns fat, adds height or works as strongly as TRT have either very weak evidence or none at all.
Chapter 3
Who benefits in trials
If you only listen to podcasts and short videos, you would think tongkat ali works for everyone. Look at the actual studies and the evidence is much narrower. It is concentrated in people whose testosterone was already low or who were under long-term stress. Several of those studies had no control group, and most of the (people are randomly split into a group taking the real thing and a group taking a placebo, and the results compared) are small.
The most solid data come from three groups: middle-aged and older men with low testosterone, stressed adults, and infertile men trying to conceive. One ring further out, sexual function, strength and lean mass show only a flicker in very small samples. For fat loss, better mood and longer life, the effect either cannot be separated from stress relief or there are no data at all.
What about healthy young men? There are a few trials, but they are few and small. Doubling a healthy 30-year-old man's testosterone is a marketing invention, not a finding.
The most solid data come from three groups: middle-aged and older men with low testosterone, stressed adults, and infertile men trying to conceive. One ring further out, sexual function, strength and lean mass show only a flicker in very small samples. For fat loss, better mood and longer life, the effect either cannot be separated from stress relief or there are no data at all.
What about healthy young men? There are a few trials, but they are few and small. Doubling a healthy 30-year-old man's testosterone is a marketing invention, not a finding.
Evidence · The three studies behind the claims
Middle-aged and older men with low testosterone. Tambi 2012 took 76 of 320 patients with late-onset hypogonadism (LOH, age-related testosterone deficiency with symptoms) and gave them 200 mg a day of a standardized water-soluble extract for 1 month. At the start only 35.5% had testosterone in the normal range; at the end, 90.8% did. On the Aging Males' Symptoms scale (AMS), the share with no complaints rose from 10.5% to 71.7%, a highly significant change (P < 0.0001). It sounds impressive, but it was a single-arm, open-label study. With no placebo group, regression to the mean (people who start low tend to test higher next time anyway) and the placebo effect cannot be ruled out, and no large trial has since repeated it. So it is a hint, not a verdict.People under heavy stress. Talbott 2013 enrolled 63 moderately stressed adults (32 men, 31 women) and randomized them to a tongkat ali extract or placebo for 4 weeks. Salivary cortisol fell 16% and salivary testosterone rose 37%, and scores for tension, anger and confusion also fell. Note that this was a stressed population with saliva testing. Salivary testosterone reflects the free fraction; in healthy people with a blood test for total testosterone, the numbers would not carry over.
Infertile men trying to conceive. Tambi 2010 gave 350 men with unexplained infertility 200 mg a day, but only 75 completed a full 3-month cycle. In those men every semen measure improved significantly on retesting, and 11 couples (14.7%) conceived naturally during the study. But this, too, was a single-arm, open-label study with no control group from a single center, and it needs independent confirmation.
tambi-2010-tongkat-ali-infertility
Evidence · The pooled analysis and weaker signals
Looking at them together: the systematic review by Leisegang 2022 included 9 studies, and 5 went into its (a combined calculation across studies). Pooled, total testosterone did rise significantly (standardized mean difference 1.35, 95% 0.57–2.14). A standardized mean difference converts different studies' units onto one common scale; by the usual yardstick this counts as large, but the interval is wide. The rise was confirmed in the hypogonadism subgroup, and trials in healthy volunteers also reported rises. The direction is positive, but the studies used very different extracts, doses and populations, and the pooled trials were all small.Further out, the evidence is thinner still. There are reports of mild improvement in sexual function and vitality in middle-aged and older people, but no direct comparison with proper erectile-dysfunction drugs. Strength and athletic performance show only a flicker in very small samples. Henkel 2014 was a pilot study in 25 physically active older adults, men and women, with no control group; it measured a rise in grip strength and did not measure body composition. Hamzah and Yusof 2003 saw a small change in lean mass in 14 people. In healthy young people who train, there is essentially no reliable signal.
Why are there so few trials in healthy young men? First, their testosterone is already normal, so it is hard to produce a clinically meaningful difference, and the trials do not pay commercially. Second, healthy people do not need it in the first place.
henkel-2014-tongkat-ali-seniors
In practice · Dose, duration, and ashwagandha
If you do use it, the usual trial dose is 200–400 mg a day of a standardized extract (Physta® or LJ100®), and the common advice is to take it in the morning on an empty stomach. Trial durations range from 4 weeks to 3 months. Do not take it continuously for more than 12 weeks; beyond that there are no data to back you.It is often compared with ashwagandha. Side by side:
Raising testosterone: both have only signals from small trials, and neither is reliable.Easing stress: both have trials showing lower cortisol.Muscle, sleep and anxiety: ashwagandha has been studied more on these.Safety: each has a weak spot. Tongkat ali rarely causes acute adverse effects but has a long-standing problem with heavy-metal contamination and adulteration; ashwagandha has a handful of reports of liver injury.
In the end neither replaces . Both are only an add-on option in situations of heavy stress or borderline testosterone.
Myth · Five mismatches in the influencer stack
When big podcast and social-media accounts promote tongkat ali, five mismatches come up again and again:Mismatch 1: applying the trial population to yourself
The strongest signals come from stressed, under-slept, middle-aged men with borderline testosterone.The audience also includes people around 25, the group with the least evidence.
Mismatch 2: the "no side effects" line
The real risk lies in product quality: reviews have documented mercury and lead contamination in commercial products from Malaysia and Indonesia."No side effects" really means "few acute side effects", not "harmless as it builds up over years".
Mismatch 3: "natural means freedom"
Quality control for supplements is generally looser than for medicines; without third-party certification, product quality is unknown.That "freedom" really means "no one is checking for you".
Mismatch 4: hinting that it can replace
Few say outright that it equals TRT, but the tone suggests natural and just as effective.The facts: the changes seen in trials are far smaller than with TRT, and the two have never been compared directly.If you really have low-testosterone symptoms that affect your life: see an endocrinologist rather than place an order online.
Mismatch 5: the more in the stack, the better
The usual recommendation is a testosterone stack of tongkat ali plus ashwagandha, Fadogia agrestis, boron, zinc, magnesium and more.No randomized trial has shown a stack works better than a single ingredient.Several substances acting on the stress axis or the sex-hormone axis, piled together, pile up side effects and interaction risks as well.
The evidence-based order of priorities (unromantic):
1. Sleep 7 hours or more: in Leproult 2011, 10 healthy young men who slept only 5 hours a night for a week had daytime testosterone 10–15% lower.
2. Control your weight, especially belly fat: the enzyme aromatase in fat tissue turns testosterone into (textbook knowledge).
3. Strength training with enough protein: improves body composition.
4. Manage long-term stress: cortisol pushes testosterone down.
5. Get checked and treated for sleep apnea (): people with severe OSA often have low testosterone.
6. Correct vitamin D if you are low: bring it up to adequate (≥ 50 nmol/L, which is 20 ng/mL).
7. After steps 1–6, if you still have symptoms and blood tests confirm a low level: see an endocrinologist for assessment; the answer may be TRT or another medicine.
"Try tongkat ali first" skips steps 1–6 and treats the add-on option from step 7 as the main road at step 0. That is marketing's core mismatch.
leproult-2011-sleep-restriction-testosterone
Chapter 4
Contamination and drug interactions
The real safety problem with tongkat ali is mostly not the molecule itself but whether the bottle you bought is clean.
At usual doses the substance itself is fairly gentle: in the studies one review pulled together, neither normal daily doses nor long-term use showed abnormal liver or kidney tests. In the first two weeks some people get insomnia, feel a bit wired or have an upset stomach, and occasionally headache or a slightly faster heartbeat. Most of this settles once the body adjusts, but there are no reliable figures for how common these reactions are. What about the long term? Honestly, no one knows. Almost every trial stops at 12 weeks, and data beyond six months are nearly blank.
The thing to worry about is heavy metals, and this is not theoretical: reviews have documented mercury and lead contamination in commercial products from Malaysia and Indonesia. These metals leave the body very slowly and build up over time, a little today and a problem years later. So here, third-party testing is not a nice extra; it is the minimum.
At usual doses the substance itself is fairly gentle: in the studies one review pulled together, neither normal daily doses nor long-term use showed abnormal liver or kidney tests. In the first two weeks some people get insomnia, feel a bit wired or have an upset stomach, and occasionally headache or a slightly faster heartbeat. Most of this settles once the body adjusts, but there are no reliable figures for how common these reactions are. What about the long term? Honestly, no one knows. Almost every trial stops at 12 weeks, and data beyond six months are nearly blank.
The thing to worry about is heavy metals, and this is not theoretical: reviews have documented mercury and lead contamination in commercial products from Malaysia and Indonesia. These metals leave the body very slowly and build up over time, a little today and a problem years later. So here, third-party testing is not a nice extra; it is the minimum.
Safety · How common contamination and fakes are
The quality of commercial products is uneven, so third-party testing (USP, NSF, ConsumerLab and similar) is the minimum here. A product without a third-party report is not automatically off-limits, but buying it is betting with your eyes closed.Alongside contamination comes adulteration. Abubakar 2018 used DNA barcoding (reading a short gene sequence to identify the species) on tongkat ali products sold in Malaysia. Only 37% were confirmed as genuine tongkat ali, and 27% were confirmed to contain other species. When eurycomanone was then checked chemically, even some products with the right species lacked this marker compound. In other words, the bottle you bought may not be tongkat ali at all, or may be the right plant without the compound it should contain. Cheap products often pass off white root or other plant roots as black root, and there is concern that some male vitality products also slip in other stimulants so that you feel something.
As for taking it continuously for a long time: whether keeping testosterone pushed up and the stress axis disturbed for long periods affects the heart and vessels, the prostate or blood thickness is unsettled. The cautious practice is 8–12 weeks on, then 4 weeks off.
abubakar-2018-tongkat-ali-adulteration
Safety · Who should not take it
A few groups should not take it, and this is not negotiable:Pregnancy, trying to conceive, and breastfeeding: it has hormonal activity, and there are no safety data at all for the fetus.People with hormone-sensitive tumors (breast, prostate, ovary, uterus): by the mechanism, it raises testosterone while holding back aromatase, and could feed the disease.People with severe liver or kidney disease: a metabolism already under strain plus heavy-metal build-up is a double risk.Children and adolescents: they are still developing, and an outside hormone modulator has no place there.People already on hormone therapy: talk with your doctor rather than adding it yourself.
Several more groups should be cautious and ideally talk with a doctor first: people taking many prescription drugs, people who have had heart rhythm problems, people with uncontrolled high blood pressure, women whose testosterone is already high (for example with polycystic ovary syndrome, ), and men with too many red blood cells (polycythemia). Pushing testosterone higher does these people no good.
Safety · Which drugs it may clash with
Drug interactions have not been studied well, but a few points are worth keeping in mind:Reports and theory suggest it may lower blood pressure and blood glucose slightly. If you take it with blood-pressure or diabetes medicines, watch for low blood pressure or low blood sugar.With anticoagulants such as warfarin it could, in theory, affect clotting, so be cautious.Most important, do not combine it on your own with , hormone replacement therapy (), clomiphene or other sex-hormone drugs: they act on overlapping steps, and things can go wrong.
Stop it two weeks before surgery, because bleeding, blood pressure and anesthesia can all be affected.
In practice · If you still want to try, in this order
If you weigh it all and still want to try, at least follow this order:1. Get a baseline first: total testosterone, free testosterone, (SHBG), , and and (the two signals the brain sends to the testes), plus a standard blood chemistry panel.
2. Ask yourself honestly whether the symptoms are real or an urge to optimize that marketing stirred up.
3. Improve sleep, exercise, weight and stress management for 4–8 weeks first.
4. If you still go ahead: choose a standardized Physta® or LJ100® extract, 200–400 mg a day, in the morning on an empty stomach. Stop after 8–12 weeks, retest at week 8, and stop if the improvement is not there.
5. Tell every doctor and dentist you see that you are taking it throughout, and stop two weeks before surgery.
In the end, anything flying a natural flag is where people most easily drop their guard. But the endocrine system is a precise feedback loop; poke it from outside for long enough and its own regulation may grow sluggish, while heavy metals build up quietly in the background. You are really running an endocrine experiment with no doctor watching, and the only participant is you.
Chapter 5
Should I use it?
The question with tongkat ali is not should I take it but am I the kind of person it might suit. Roughly four groups are worth considering:
Men over 35 whose blood tests confirm total testosterone near the bottom of the normal range, who have low libido, fatigue or low mood, and who do not want : first spend 4–8 weeks on lifestyle changes. If nothing improves, try a standardized extract at 200–400 mg a day and retest testosterone and symptoms after 8 weeks.Men with diagnosed late-onset hypogonadism (LOH) who cannot or will not use TRT: discuss it with an endocrinologist as an add-on.People under long-term stress who feel their libido and energy have dropped: a trial of 8 weeks is reasonable, and any benefit may come mainly from lower cortisol.As an add-on for male infertility: there are only signals from studies without a control group. Decide together with a fertility specialist; it does not replace proper treatment.
For healthy young men, for anyone hoping to use it as the main treatment, during pregnancy or with a hormone-sensitive tumor, and for women, it is either not worth using or should not be used.
Men over 35 whose blood tests confirm total testosterone near the bottom of the normal range, who have low libido, fatigue or low mood, and who do not want : first spend 4–8 weeks on lifestyle changes. If nothing improves, try a standardized extract at 200–400 mg a day and retest testosterone and symptoms after 8 weeks.Men with diagnosed late-onset hypogonadism (LOH) who cannot or will not use TRT: discuss it with an endocrinologist as an add-on.People under long-term stress who feel their libido and energy have dropped: a trial of 8 weeks is reasonable, and any benefit may come mainly from lower cortisol.As an add-on for male infertility: there are only signals from studies without a control group. Decide together with a fertility specialist; it does not replace proper treatment.
For healthy young men, for anyone hoping to use it as the main treatment, during pregnancy or with a hormone-sensitive tumor, and for women, it is either not worth using or should not be used.
In practice · When to skip it, and how to judge it
Situations where it is not worth it or not recommended:① Healthy men aged 25–35 who want to optimize testosterone
The trial signal in this group is weak; baseline testosterone is already normal, and negative feedback limits how far it can rise.Putting the money and effort into sleep, training, protein and diet pays back far more.
② The influencer stack (tongkat ali plus Fadogia, zinc, boron and ashwagandha)
No randomized trial has tested the stack; side-effect and interaction risks pile up, and it is not cheap.Trying one thing for 8 weeks and then retesting tells you far more than running the whole stack.
③ Severe erectile dysfunction, clearly low testosterone or infertility, with tongkat ali as the main treatment
The rise is not enough; see urology, a fertility specialist or endocrinology.Tongkat ali is acceptable as an add-on, not as the main treatment.
④ Any pregnancy plans, breastfeeding, or a hormone-sensitive tumor: do not use it.
⑤ Women wanting higher testosterone
Healthy women already sit in a low range, and it should not be adjusted from outside.Women with polycystic ovary syndrome (), excess hair growth or naturally high testosterone: do not use it (it may make things worse).For stress relief, choose ashwagandha or rhodiola rather than tongkat ali.
If you decide to use it, how to choose a product:
A standardized extract labeled Physta® or LJ100® that states its eurycomanone content: the trial data come from products like these.A third-party heavy-metal test report showing none detected.USP, NSF or ConsumerLab certification.Unstandardized pure tongkat ali powder: be wary.Blends sold for male vitality: not recommended, because you cannot tell which ingredient is doing anything.
Typical dose and cycle: Physta® 200–400 mg a day, in the morning on an empty stomach, in cycles of 8–12 weeks with 4–8 weeks off before starting again. Test testosterone, , and before you start and at week 8, and write down how you feel.
"It really makes me feel better" can mean one of two things:
1. It really works: testosterone rises and cortisol falls, and you feel the difference.
2. Placebo plus trust: you trust whoever recommended it, you paid for it, and you expect to feel better, so your self-ratings naturally rise.
How do you tell them apart? Measure objectively before you start and at week 8 (a blood test for testosterone plus a symptom questionnaire). If the objective measures have not changed but you feel better, the placebo effect is at work. Feeling better still has value, but be honest with yourself.
In the end: for the stressed, borderline-testosterone group, tongkat ali is a defensible add-on option. It is not a cure-all that raises every man's testosterone, not a substitute for , and not a casual tool for optimizing your body, and it carries real risks: contamination, drug interactions and missing long-term data. In the right situation, with measurement and a time limit, it has a place. In the wrong situation, taken long-term because it is fashionable, you will most likely have spent money, taken on risk and fooled yourself.
References · 4
- Rehman, S. U., Choe, K., & Yoo, H. H. (2016). Review on a traditional herbal medicine, Eurycoma longifolia Jack (Tongkat Ali): its traditional uses, chemistry, evidence-based pharmacology and toxicology. Molecules, 21(3), 331. Reviews documented mercury and lead contamination in Malaysian and Indonesian tongkat ali commercial preparations. 10.3390/molecules21030331
- Talbott, S. M., Talbott, J. A., George, A., & Pugh, M. (2013). Effect of Tongkat Ali on stress hormones and psychological mood state in moderately stressed subjects. Journal of the International Society of Sports Nutrition, 10(1), 28. 63 moderately stressed adults (32 M / 31 F), 200 mg/day Eurycoma longifolia × 4 wk → **salivary** cortisol ↓ 16% and **salivary** testosterone ↑ 37% vs placebo; tension ↓ 11%, anger ↓ 12%, confusion ↓ 15%. Note the assay: salivary testosterone tracks the free fraction, so this is not evidence of a 37% rise in serum total testosterone. 10.1186/1550-2783-10-28
- Tambi, M. I. B. M., Imran, M. K., & Henkel, R. R. (2012). Standardised water-soluble extract of Eurycoma longifolia, Tongkat ali, as testosterone booster for managing men with late-onset hypogonadism? Andrologia, 44(s1), 226-230. Single-arm, open-label (no placebo control); 76 of 320 screened late-onset-hypogonadism men were treated 200 mg/day × 1 month, after which 90.8% reached normal serum testosterone (P < 0.0001). No control arm — regression to the mean and placebo effect cannot be excluded. Before treatment 35.5% had normal testosterone and 10.5% had no complaint on the Ageing Males' Symptoms scale; after 1 month the figures were 90.8% and 71.7% (abstract, PMID 21671978). 10.1111/j.1439-0272.2011.01168.x
- Leisegang, K., Finelli, R., Sikka, S. C., & Panner Selvam, M. K. (2022). Eurycoma longifolia (Jack) improves serum total testosterone in men: a systematic review and meta-analysis of clinical trials. Medicina (Kaunas), 58(8), 1047. 9 studies in the systematic review, 5 RCTs in the meta-analysis. A significant rise in total testosterone was mostly reported in both healthy volunteers and hypogonadal men; pooled SMD 1.352 (95% CI 0.565-2.138, p = 0.001), confirmed in the hypogonadism subgroup. SMD is a standardized effect size, not a change in ng/dL; the authors say more research is required before clinical use (abstract, PMID 36013514). 10.3390/medicina58081047