Editor's Note
  • February 22, 2018 - Since our last review, the manufacturers of two of our top picks have gone out of business, and some new testosterone boosters have entered the arena. We’ve updated this review to evaluate the current field of testosterone supplements, as well as beef up analysis on what kind of results you can expect from t-boosters. Our only current top pick, Beast Sports Nutrition, is a new player in the industry that contains all four of the ingredients with studies showing a positive effect on testosterone.

We’ll be honest. Testosterone boosters don’t really boost. The best testosterone booster is like taking a multivitamin with extra herbs that might slightly and temporarily increase your testosterone levels. Like all supplements, finding the right testosterone booster means wading into a sea of ingredients, all promising to help. Of 133 testosterone boosters, we found only one with the right ingredients to help raise your testosterone levels: Beast Sports Nutrition - Super Test ($45.88 for 180 capsules, or $2.04 per day).

Beast Sports Nutrition - Super Test has all four of our dream ingredients: magnesium, fenugreek, longjack, and zinc. These ingredients have all been demonstrated to help increase natural testosterone levels, with plenty of scientific research to support them (done on humans too, and not just rats). By combining all four ingredients, Super Test has the best chance of helping to increase your testosterone levels, and thereby helping you gain muscle or have a more active sex life.

This doesn’t mean Super Test is perfect — we take a closer look at some of its ingredients below — but it beats out the competition. Every other supplement we looked at either didn’t have all four ingredients, overdosed us on vitamins or minerals (a good way to develop kidney and liver problems), contained ingredients that would harm us, or some combination thereof.

Do testosterone boosters work?

Testosterone boosting vs. anabolic steroidsEven if the goal is the same (more testosterone), there’s a key distinction in method. With steroids, you’re putting more testosterone into your body from an outside source. With boosters, you’re trying to trick your body into making more testosterone on its own.

We should probably start with the elephant in the room: do these supplements increase testosterone? The answer is probably yes. There are some ingredients that help convince your body to produce more testosterone, but there’s a catch. Testosterone boosters aren’t actually great at boosting; that is, at pushing your testosterone levels above your healthy, normal balance. Boosters typically act more like restorers — helping bring low testosterone levels back to that healthy equilibrium rather than boosting you above normal testosterone levels. Just like how if you have anemia, taking a vitamin B12 supplement can help restore your energy and reduce fatigue, but if your B12 levels are good, a supplement won’t give you super energy levels to stay awake for three days — your body will likely just process (read: pee) out the extra.

This is because your body is really good at self-regulating your hormone levels. So if you have normal testosterone levels, boosting above your natural base level may at best give you a few hours while your body makes, and then immediately processes out, the excess testosterone. This means you might experience higher than your average testosterone levels, but not by much, and only for a little while.

Is a testosterone booster right for me?

Dr. Darryn Willoughby, a professor of health, human performance and recreation and the director of the Exercise and Biochemical Nutrition Laboratory at Baylor University, told us that even in studies where there was an increase in testosterone, it was only around 15–20 percent. “In men with clinically normal testosterone levels, this modest increase will most likely not be anabolic enough to improve exercise performance,” he says. So if you have normal testosterone levels, and are simply trying to get an extra edge in gaining muscle, losing weight, or some extra time in the bedroom — you might see some results from taking a testosterone booster. But really, these will be most useful for men with low testosterone trying to get back to a healthy testosterone range.

How do I know if I have low testosterone?Symptoms can vary depending on your age, and we recommend checking out the Mayo Clinic’s guide for specifics. If you are suffering from any of these symptoms, you need to see a doctor, since low testosterone can be a sign of a serious medical condition.

Your first step should be to see your doctor. If you think you have low testosterone, we cannot stress enough that you should proceed with caution and talk to a medical professional — taking a booster can definitely do more harm than good. Low testosterone can be a symptom of more serious problems, like a pituitary disorder or a side-effect of medication, and a booster can mask the root cause. A doctor will be able to evaluate your testosterone levels with a simple blood test, and if you both decide a booster is the way to go, give the ingredients of any supplement a once-over to make sure that they’re not at risk of making your personal health situation worse.

Bottom line: testosterone boosters aren’t right for a lot of people. We dive deep into ingredient research below, but typically, testosterone boosters contain at least one (and often three or more) different ingredients that each impact your circulatory system — both the heart and blood. If you’re taking any kind of blood-thinner medication, or you have a history of heart disease, these supplements can get really dangerous, really quickly. The simple fact of the matter is that hormones are tricky things to mess with, and a doctor should be your first port of call to help you safely achieve your goals — whether they’re related to fitness, weight, or libido.

How We Found The Best Testosterone Booster

To find the best testosterone booster, we collected every supplement available on BodyBuilding.com, and cross-checked our list against the top results on best of lists like MensFitness, BroScience, and BodyNutrition. We only looked at pills since some of the ingredients in testosterone boosters have a reputation for tasting bad, and powders just prolong the experience. There are a lot — 133 of them to be precise — and they all claim to boost testosterone levels. Testosterone (for men) is “thought to regulate sex drive (libido), bone mass, fat distribution, muscle mass and strength, and the production of red blood cells and sperm.” If a supplement can increase your natural testosterone levels, the rest should follow. As we mentioned above, it’s not that simple, and at best, you’ll experience only a short-lived boost.

This doesn’t mean taking boosters every few hours.Just because any effects you might see wear off in a couple hours doesn’t mean you should take them every few hours (as some websites suggest). Boosters have ingredients in them with daily maximum caps — like vitamins — that will damage your kidneys if you take them in excess.

Even so, it’s possible to have some benefit by taking a testosterone booster. To find the best, we dug into the scientific literature to find out which ingredients had the best chance of increasing human testosterone levels, and which ones are still being investigated in eels or stressed chickens.

We kept it simple, and followed the premise of testosterone boosters: testosterone affects muscle gain, weight loss, and libido, so by increasing the amount of testosterone in the body, we can improve on each of those goals. This meant that we looked for ingredients proven to increase testosterone levels, not ingredients that might increase libido or help build muscle mass independently of testosterone (like having a healthy diet and feeling good about yourself). In addition, we dove deep into the specific ingredient lists of our finalists and cross-checked them against WebMD and the National Institutes of Health (NIH) database to make sure that they did not contain ingredients known to be harmful.

We did not look at anabolic steroids.

Anabolic steroids increase testosterone, but we didn’t look at them because they require a doctor’s prescription and tend to have greater undesired side-effects.

Using steroids eventually trains your body to realize that it doesn’t have to produce as much testosterone to reach its equilibrium, so to reach the same highs you’ll need to take more steroids, and when you stop taking them, your body will need to readjust — you’ll be living with low testosterone for a while (and you’ll need to see a doctor if your body doesn’t readjust on its own). Forcing your body to stay above your natural testosterone, even if you’re naturally low, can create this kind of dependency which ultimately decreases the amount of testosterone your body will produce on its own.

We found four ingredients worthy of their hype: magnesium, fenugreek, longjack, and zinc.

Looking for ingredients that work in the realm of supplements can be like finding a needle in a haystack. Testosterone boosters, like all dietary supplements, are not approved by the Food and Drug Administration prior to marketing. This lack of oversight dates back to the 1994 Dietary Supplement Health and Education Act (DSHEA), which stipulated that purveyors of supplements weren’t required to prove the safety of their products or the veracity of what’s on the labels to the FDA before listing them for sale. Often, there isn’t a lot of scientific backing behind an ingredient, or research has been done solely on animals, not humans.

We scoured the database of the National Center for Biotechnology Information (part of the U.S. National Library of Science) for articles. Of the many ingredients marketed as boosting testosterone levels, we only found four backed by multiple articles based on human testing. For the best chance of boosting testosterone levels, a supplement needs to contain magnesium, fenugreek, and longjack — and some zinc wouldn’t go astray, either.

Eating well is your first step to building muscle and feeling well.

In many of the studies we found, those who saw the most improvement in health, testosterone, or muscle gain were those with existing nutrient or vitamin deficiencies. This means that some gains may be due more to dietary changes and generally restoring nutrient and vitamin levels than any one magic ingredient, but also that making sure your diet includes healthy amounts of nutrients should be your first step.

We required magnesium: a key ingredient for muscle building.

Magnesium is an essential mineral all on its own. It supports your immune system and helps “maintain normal nerve and muscle function” and everyone should (boosting aside) make sure they’re getting enough of it. It’s commonly found in food, meaning it’s pretty difficult to develop a magnesium deficiency.

That said, magnesium is one of a few ingredients demonstrated to impact testosterone levels. Researchers at Italy’s University of Palermo found that magnesium improved participants’ anabolic hormone status — including their testosterone levels. In a follow-up study, they confirm that even adjusting for age differences in their participant group, “magnesium was positively associated with total testosterone.” They propose that magnesium supplementation might help improve muscle performance in aging men — a group particularly vulnerable to declining/low testosterone levels. Outside of Italy, researchers at Turkey’s Selçuk University found that magnesium supplementation increased testosterone levels for both athletes and more sedentary men alike.

We required all of our testosterone boosters to have magnesium, but gave preference to magnesium aspartate, citrate, lactate, and chloride. These forms have been found to be more easily absorbed than magnesium oxide and sulfate. (On the other hand, it didn’t count if the supplement had magnesium stearate, which is used to make pills not stick together.)

We cut 22 testosterone boosters without magnesium.

AllMax Nutrition – Testo FX
Black Lion Research – Viron
Cellucor – P6 Original
Defiance – Testosterone Booster
EPG – Tetroshred
FINAFLEX – Revolution Test
Irwin Naturals – Steel-Libido
Irwin Naturals – Testosterone UP
JYM Supplement Science – Alpha JYM
Labrada – HumanoGrowth
Magnum Nutraceuticals – Thrust
Magnum Nutraceuticals – Tonic
MRM – DHEA
MuscleTech – Test HD Super Elite
Nugenix
NutraBio – 100% Pure Tribulus
Nutrex – TESTED
Olympian Labs – DHEA
S.A.N. – Tribuvar
Testogen
Transform Supplements – Forged Methyl EAA
USN – Testo Max 17

We also required Fenugreek (Trigonella foenum-graecum), which boosts libido.

Watch out for ingredients that interfere with blood clottingIf you are taking any kind of blood medication, take aspirin or ibuprofen, or have any kind of blood-related condition, you’ll want to consult your doctor before taking any of these supplements. Fenugreek, Forskolin, and Acetyl-L-carnitine are just a few of the ingredients that can make these situations worse and increase your chances of bruising and bleeding.

Fenugreek is often found in Indian, Turkish, and Persian cuisine. Multiple studies have found it to improve testosterone levels, and in particular, sexual performance. Scientists at Babu Banarasi Das University and King George’s Medical University in India have found that fenugreek improved testosterone levels. Testosterone levels increased for 90% of the volunteers, sperm morphology (the size and shape of sperm) improved for 14.6%, and more than 50% of volunteers experienced improvements in mental alertness, mood, and libido.

Getting even more specific, the University of Sydney in Australia found that in addition to testosterone levels increasing, men experienced a higher number of morning erections, and had sex more often after taking a dose of 600mg per day for 12 weeks. (It also improved sex drive in women, too.)

While researchers in Brisbane, Australia, found that while Testofen (“a standardized [fenugreek] extract and mineral formulation”) significantly improved the sexual arousal, orgasm, and the general quality of life of participants, it did not remarkably increase testosterone above normal levels. Participants who took Testofen were more satisfied with their energy, well-being, and muscle strength than those who took the placebo.

We cut 82 testosterone boosters without fenugreek.

AllMax Nutrition – TribX 90
AllMax Nutrition – ZMA
AST – DHEA 100
Axis Labs Hypertest XTR Testosterone Complex
Betancourt Nutrition – Androrush
Blue Star Nutraceuticals – GH Peak
Bodybuilding.com – Signature ZMA
Bodybuilding.com Foundation Series – Tribulus Terrestris
Cellucor – P6 PM
Controlled Labs – Blue Gene
Controlled Labs – Blue Up
Controlled Labs – Blue Up – Stim Free
Core Nutritionals – Hard
Defiance – Forskolin
Dymatize – Z-Force
EVLUTION NUTRITION – ZMATRIX
Formutech Nutrition – Recover
GAT – JetFUEL T-300
GAT – Mens Multi+Test
GAT – Tribulus
Gen X Labs – TestABOL
Healthy ‘N Fit – Advanced Steroidal Complex
iForce Nutrition – Intimidate SRT
iForce Nutrition – Reversitol V2
iForce Nutrition – Testabolan
iForce Nutrition – Tribulus 2400
iForce Nutrition – ZMA
IronMagLabs – Anabolic Matrix
JYM Supplement Science – ZMA JYM
LiveLong Nutrition – Forskolin
LiveLong Nutrition – Icariin
MAN – N-XT
MHP – Super ZMA Test
MRM – Tribest 750
MuscleMeds – Methyl Arimatest
MusclePharm – Z-Core PM
MuscleTech – Platinum 100% Tribulus
MuscleTech – Test 3X SX-7 Black Onyx
MuscleTech – TEST HD
MuscleTech – Vitamax Test SX-7 Black Onyx
Natrol – DHEA
NOW – Men’s Virility Powder
NOW – TestoJack 100
NOW – Tribulus
NOW – ZMA
NutraBio – ZMA
Nutrabolics – Aggro
Nutrex – T-UP
Olympian Labs – Dynamic HGH
Olympic Labs – Test1fy
Optimum Nutrition – Tribulus
Optimum Nutrition – ZMA
PEScience – TruZMA
PharmaFreak – ANABOLIC FREAK
PharmaFreak – ANDRO FREAK
PrimaForce – ZMA
Prime Male
Prolab – Horny Goat Weed
RSP Nutrition – Z-Elite
S.A.N. – Alpha Impact
S.A.N. – DHEA
S.A.N. – FREE-T
S.A.N. – MyoTEST
S.A.N. – Testo Hardcore
S.A.N. – Tribuvar 1000
S.A.N. – Zinc Magnesium Aspartate
Six Star Pro Nutrition – Testosterone Booster
SNAC – ZMA
SNAC – ZMA-5
Supreme Sports Enhancements – Androgenix
Supreme Sports Enhancements – Omnibolic
TESTOBOOST Test Booster Supplement
Twinlab – Tribulus Fuel
Twinlab – ZMA Fuel
Universal Nutrition – Natural Sterol Complex
Universal Nutrition – Tribulus Pro
Universal Nutrition – ZMA Pro
Vigor Labs – Black Antler
Vigor Labs – Raw IGF-1
Vigor Labs – Wrecking Balls
VINTAGE BOOST – Wave-Loaded Testosterone Booster – Fast-Acting, Safe & Effective Supplement
Vitalabs – Explosive DAA Max

And we required Longjack (Eurycoma longifolia), another libido booster.

Longjack, also known as Tongkat ali and pasak bumi, is a shrub hailing from Southeast Asia purporting to improve libido. It’s gaining traction in the scientific community for potentially increasing testosterone levels, and researchers at South Africa’s University of the Western Cape found that longjack improved testosterone levels and muscular strength in physically active seniors (a population with typically low testosterone).

What is TRT? Testosterone Replacement Therapy (TRT) uses artificial androgens (think synthetic steroids) to try and raise testosterone levels. As the Mayo Clinic notes, they’re still being evaluated for safety and effectiveness, but it’s an option to discuss with your doctor.

Other researchers at the National University of Malaysia have gone so far as suggesting that, after further study, longjack could be used as an alternative approach to testosterone replacement therapy (TRT).

That said, a group of researchers at the National University of Malaysia did a systemic literature review of longjack, looking for clinical research that demonstrated a relationship between the shrub and testosterone levels. Of 150 articles, only 11 met their inclusion criteria — involving humans and scientifically rigorous. However, of those 11 studies, seven “revealed remarkable association” between using longjack and improving male sexual health, while the remaining four “failed to demonstrate sufficient effects.” The team concluded that longjack looks “promising” when it comes to raising low testosterone, and that there is convincing evidence that it works.

We cut 22 testosterone boosters without longjack.

Ageless Foundation – Ultra T Gold
Betancourt Nutrition – TEST-HP
Blackstone Labs – Apex Male
Cellucor – P6 Chrome
Cellucor – P6 Ripped
EVLUTION NUTRITION – EVL Test
Evlution Nutrition Testosterone Booster Pills EVL Test Training & Recovery Amplifier
Force Factor – Test X180
Force Factor – Test X180 Alpha
Force Factor – Test X180 Ignite
Force Factor – Test X180 Tempest
Human Evolution – Test Ignition
Infinite Labs – Elevate Cyclo Test
MAN – Delta XT
MuscleTech – Pro Series Alpha Test
Novex Biotech – TestroVax
PharmaFreak – TEST FREAK
RSP Nutrition – Prime- T
Tek Naturals – TestoTEK
TestoFuel
True GRIT – Test Booster
Universal Nutrition – N1-T

We wanted the best testosterone booster to contain Zinc — an important mineral for fertility.

Zinc is little more of a nice-to-have ingredient than a must-have. It’s on our radar as an ingredient that possibly boosts testosterone levels, and while we couldn’t find enough supporting evidence that taking zinc would increase natural testosterone, low zinc levels have been connected to infertility. A low zinc level is also possibly a sign of hypogonadism. The closest support we found is in a study which found that people recovered from nutritional deficiency-related problems more quickly if they took a zinc supplement than those who did not. Zinc is available in many foods, such as oysters, fortified breakfast cereals, and red meat.

We didn’t cut any contenders for not having zinc (by this stage, all of our finalists did). However, it’s possible to have too much of a good thing, and one product got cut for having too much zinc (read on).

Finally, we took a hard look at dosages and proprietary blends.

Several of our finalists tripped up on dosage.

Every ingredient can be harmful when taken in significant quantities (we go more into that below), so we pored over each booster’s ingredient list to make sure that they weren’t serving up an overdose. In particular, we took a close look at magnesium and zinc, which have enough scientific background behind them to offer hard upper limits on how much you can safely consume.

What about fenugreek and longjack?Not enough is known about longjack to suggest at what level it will become harmful, and fenugreek levels have only been studied for diabetes and menstruation. We recommend working with your doctor to determine whether you’re developing unwanted side-effects from these ingredients.

Magnesium comes with a strict upper cap. Excess magnesium is hard on your kidneys, and can lead to kidney failure. The NIH recommends that men consume 400-420 mg of magnesium daily, but that they should not exceed 350 mg of supplemental magnesium per day. Because while it’s rare for people to chronically overdose on magnesium through diet (you’d have to eat a lot of almonds and spinach, for example), overdose by supplement is far more common.

We reviewed the ingredient lists of our supplements and cut three that prescribed us an overdose of magnesium. While it’s possible to stay under the 350mg daily limit of supplemental magnesium by taking fewer pills than the manufacturer recommends, we were concerned that any manufacturer would advise you to exceed the recommended safety limit for magnesium intake by almost a third.

We cut 3 products with too much magnesium.

GAT – Testrol
Blue Star Nutraceuticals – Status
GAT – Testrol Gold ES

Zinc also has an upper limit. The NIH recommends that adults should not take more than 40mg of zinc per day, and notes that even moderately high zinc intake levels can be harmful. We cut MHP’s Clinical Strength T-Bomb 3Xtreme for having too much zinc — 50mg per daily serving.

We cut 1 product with too much zinc.

MHP’s Clinical Strength T-Bomb 3Xtreme

This left us with three testosterone boosters with magnesium and zinc amounts below the NIH’s recommended thresholds:
Assault Labs - Sergeant Steel
Beast Sports Nutrition - Super Test; and
iSatori - ISA-Test GF.

Two finalists contained potentially dangerous ingredients.

Finally, we looked at the proprietary blends of our remaining boosters, and dug into their ingredient lists. Supplements frequently include ingredients known for their “folk-lore” value; they’re believed to work, even when there isn’t any scientific background to prove it. Though we didn’t ding points if an ingredient wasn’t proven to be good (just so long as it wasn’t proven to be bad), we didn’t want to include any ingredient with evidence of causing harm.

Sergeant Steel ran into trouble here because it contains Shilajit — a type of plant-based resin. Shilajit is banned in Canada because the Canadian government found heavy metal levels when investigating the ingredient. Shilajit is hard to find, and sensitive to water and variations in temperature, so most manufacturers mix it with additives to make it more stable. Research at Boston University School of Medicine found that “nearly 21 percent of 193 ayurvedic herbal supplements [...] contained lead, mercury or arsenic,” and included shilajit on the list of contaminated ingredients. Even though Sergeant Steel lists its shilajit is “purified,” it doesn’t offer any third-party testing to confirm whether or not their shilajit contains heavy metals, and so we cut it.

Both Beast Sports’ Super Test and iSatori’s ISA-Test contain a proprietary blend, which means they don’t disclose the amount of each and every ingredient in the mix. This is only a problem if there is an ingredient tucked into a proprietary blend for which we need to know an amount, like magnesium and zinc. While none of the ingredients in Beast Sports’s proprietary blend raised any red flags, iSatori’s blend contains melatonin, a hormone that helps regulate sleep. Melatonin is an ingredient that has a hard upper limit — Healthline suggests at most 10mg for an adult — and even lower doses can interact poorly with many medications. Since we can’t confirm whether the amount of melatonin in iSatori’s proprietary blend is under 10mg, we cut iSatori.

This left us with one testosterone booster:

Our Top Pick for The Best Testosterone Booster

Best Overall
Beast Sports Nutrition - Super Test
Beast Sports Nutrition
$45.88 for 180 capsules, or $1.02 per serving, but it’s two servings per day, so $2.04 per day.

Beast Sports Nutrition’s Super Test contains our complete quadfecta of ingredients: magnesium, fenugreek, longjack, and zinc, which means it should give you the best chance at increasing your testosterone levels.

It also has vitamin B6. One study called out folate and vitamins B6 and B12 as important nutrients for athletes to achieve optimal health and performance. Vitamin B6 is commonly found in food, like fortified cereals, and as with magnesium, it’s possible to have too much vitamin B6. The NIH recommends an upper daily limit for adults of 100mg per day. Beast Sports comes well under this limit at 10mg per day, but still well above the minimum recommended dose of 1.7mg needed to see benefits.

We do note that Beast Sports’ supplemental magnesium level is fairly low — 26 mg per serving, up to 52 mg per day. If your diet is not particularly rich in magnesium (found in leafy greens, nuts, and whole grains), Beast Sports may not give you enough to meet the daily recommended dose. However, if you’re taking other multi-vitamins or supplements with magnesium, you’re less likely to cross that 350mg daily upper limit.

Beast for Testosterone Booster

Beast Sports recommends taking four capsules twice per day. The pills are about the same size as a multivitamin or a Tylenol liquid gel pill — not tiny tablets, unfortunately, but they aren’t horse pills. They smell like the boxes of raisins your Mom packed into your school lunch, but stale, like they were forgotten in the pantry for a few years, and a little spicy, like she sprinkled curry powder on them. If you follow this eight pills per day regime, your $46 bottle will last you twenty-two days, and cost you about $2 per day.

Like most supplements, Beast Sports contains several ingredients with little research about their long-term effects. WebMD describes Suma powder, Rhodiola Rosea, Cissus quadrangularis, Tribulus extract, and ashwagandha extract as possibly safe when taken for a short period of time (usually around 6-10 weeks). However, their long-term safety remains unknown. It also has a few ingredients, like cyanotis vaga root, safed musli, and polygonum cispidatum root extract for which there is a lack of data on even short term safety.

It’s important to consult your doctor before adding any supplement into your routine, but we wanted to call out a few ingredients in Beast Sports’ Super Test that you want to be particularly aware of. We’ll dive into the specifics below, but here’s the general breakdown*:

Tribulus terrestris — consult your doctor if you take lithium or medications for diabetes

Ashwagandha — consult your doctor if you take immunosuppressants, sedatives, or thyroid medication

Polygonum cuspidatum — consult your doctor if you take medications that are changed and broken down by the liver, or medications that slow blood clotting.

Chasteberry Tree extract — consult your doctor if you take antipsychotics or drugs for Parkinson’s disease.

*This is NOT a full list of ingredients with potentially harmful interactions or side-effects. We advise you to consult your doctor to make sure this supplement can be integrated into your diet without harm.

What are safe ingredients?

Ingredients that don’t live up to the hype.

We came across some ingredients that testosterone boosters like to promote as helping increase testosterone that don’t actually have the scientific proof to back the claim. If you were looking for any of these ingredients, here’s why we didn’t feature them as requirements, and why you might want to watch out for them.

Ashwagandha is sometimes included in testosterone supplements because of the hypothesis that it improves fertility. However, we couldn’t find sufficient evidence to support this claim (at best, one study found that ashwagandha might improve cardiorespiratory endurance). WebMD advocates caution when taking this herb, as it may interact with immunosuppressants, sedative medications, and thyroid hormone medications.

Epimedium (a.k.a horny goat weed) has been demonstrated to increase testosterone levels, but so far, only in rats. WebMD again does not make any dosage recommendations, and warns that horny goat weed can interact poorly with medications for high blood pressure and ones that slow blood clotting.

Grape seed extract is another ingredient with not enough research to suggest a dosage. Grape seed extract can interact with drugs like “blood thinners, NSAID painkillers (like aspirin, Advil, and Aleve), certain heart medicines, cancer treatments, and others.” If this sounds like you (or if you ever pop an Advil to clear off a headache), you’ll need to speak with a doctor to make sure this supplement is safe to take.

Japanese Knotweed (a.k.a Hu Zhang or Polygonum cuspidatum) is highlighted by WebMD as needing more evidence to rate its effectiveness in a number of different areas: like treating constipation and liver or heart disease. They also warn that it can interact poorly with medications that are changed and broken down by the liver, and those that slow blood clotting (anticoagulants and antiplatelets).

Mucuna pruriens (a.k.a velvet bean extract or cowhage) has red flags for having major interactions with medications taken for depression, and some medications for high blood pressure. It can also interact poorly with medications for diabetes and mental health conditions.

Tribulus terrestris is an ingredient commonly presented as improving testosterone levels, but has not been found to be more effective than a placebo or possess any testosterone increasing properties. WebMD cautions that it interferes with Lithium and diabetes medications, and in general, not enough is known about tribulus terrestris to recommend a dosage for anyone.

Even safe ingredients can be harmful at higher dosages.

Every vitamin, mineral, and ingredient that affects the human body can be taken in enough quantities that they are harmful, or toxic, even the ones that — at lower levels — are beneficial or necessary. Unfortunately, testosterone boosters contain a lot of ingredients that are not well understood. This means in addition to not being able to confirm whether certain ingredients increase testosterone, the scientific and medical communities also don’t know at what levels many ingredients become toxic. On the up side, you might need to eat several pounds of a particular leafy plant before it becomes harmful. On the down side, it could be significantly less that pushes you over your body’s limit. We simply don’t know how little or how much the human body can tolerate. We recommend keeping your doctor in the loop when you add any supplement with unproven ingredients into your diet — they’ll be able to help you find and track any undesired side-effects that these ingredients might cause.