How to Read a Supplement Label: Proprietary Blends and Red Flags

Buying guideBy Marcus Hale · Published 7 October 2026 · Last reviewed 7 October 2026

Most testosterone boosters are sold on their front label: big promises, a few ingredient names, a bold number. The truth is on the back, in the Supplement Facts panel. I'm not a doctor, and this is not medical advice. This is how I read that panel, and what the research says about what you'll find.

What does a supplement label have to show?

In the US, dietary supplement labels must carry a Supplement Facts panel with the serving size, the number of servings per container, a list of all the dietary ingredients and the amount per serving. One thing people often miss: the FDA does not approve supplements for safety or effectiveness before they are sold, and it does not approve their labeling either. The companies themselves are responsible for making sure their products meet the rules (FDA 101: Dietary Supplements).

So the label is the company's own statement. Reading it carefully is the main check you have.

What is a proprietary blend?

It is a legal way to list several ingredients together. Under the FDA's labeling rule, a blend gets its own name, the amount shown is the total weight of everything in the blend, and the ingredients are listed underneath in descending order of predominance by weight. The rule does not require the amount of each individual ingredient (21 CFR 101.36).

Why does a hidden dose matter?

Because studies test specific doses of specific extracts. Here are three I've covered:

• The tongkat ali study used 200 mg a day of a standardized water-soluble extract.
• The ashwagandha trial used an extract delivering 21 mg of withanolide glycosides a day.
• A fenugreek trial used 600 mg a day of a standardized seed extract for 12 weeks.

If a label says "Testo Blend, 1,200 mg" and lists all three, you can't know whether you get the study dose or a pinch. A pinch is cheaper, and the front label can still quote the study.

What do testosterone booster labels look like in practice?

A 2020 study in The World Journal of Men's Health looked at 50 "T booster" supplements found through a Google search. The researchers checked each product's ingredients and claims, then searched PubMed for human data on each ingredient (Clemesha et al., 2020).

• The claims: 90% of the products claimed to "boost T", 50% to "improve libido" and 48% to "feel stronger".
• The ingredients: 109 different ones, an average of 8.3 per product.
• The evidence: only 27 of the 109 ingredients (24.8%) had data showing higher testosterone. For 67 of them (61.5%) the researchers found no studies on testosterone at all.
• The doses: the median product contained 1,291% of the recommended daily amount of vitamin B12, 807.6% of B6 and 272% of zinc. Thirteen of the 50 products went over the FDA's upper limit for zinc, vitamin B3 or magnesium.

I don't read this as "every booster is useless". I read it as: the ingredient list is where the marketing gets ahead of the evidence, so the list is where you should look hardest.

Which claims and label details are red flags?

• A "proprietary blend" that covers the main ingredients. If the stars of the product are inside the blend, you can't check the dose.
• Claims that the product treats, cures or prevents a disease. The FDA says that a product intended to treat, prevent, cure or alleviate the symptoms of a disease is a drug, even if it is labeled as a supplement. "Treats low testosterone" is a drug claim.
• "FDA approved". The FDA doesn't approve supplements before sale. It also doesn't approve facilities, so "made in an FDA-approved facility" is misleading (FDA on hidden ingredients).
• Megadoses. Several times the daily amount of a vitamin or mineral is not a feature. See the zinc, vitamin B3 and magnesium findings above.
• Big promises about libido, strength or "performance". I'll explain why below.
• No named manufacturer and no way to contact them. If you can't find who makes it, you can't ask who tested it.
• "Clinically proven" with no study named. A real claim links to the study, and the study tested that ingredient at that dose.

Can a product contain drugs that are not on the label?

It happens, and it is one more reason to be careful with this category. The FDA keeps a database of products marketed as dietary supplements that turned out to contain unapproved drug ingredients. A study of that database for 2007 to 2016 counted 776 such products. Most were sold for sexual enhancement (353 products, 45.5%), weight loss (317, 40.9%) or muscle building (92, 11.9%). Among the muscle-building products, 82 of 92 (89.1%) contained synthetic steroids or steroid-like ingredients (Tucker et al., 2018).

This does not mean most testosterone boosters contain hidden drugs. These are only the products the FDA caught. But it shows where the problem tends to show up. The FDA's own advice is to be especially wary of products sold for sexual enhancement and energy, weight loss, pain, bodybuilding or sleep, and to talk to a health professional before trying a new supplement.

What is my label checklist?

This is the same list I use for the buying checklist in my main guide, with the reasons spelled out.

1. Every key ingredient has its own amount. No "blend" hiding the headline ingredient.
2. The dose matches a study. Compare the extract and the milligrams with the research before you pay.
3. No vitamin or mineral megadoses. Check the numbers against the upper limits.
4. A named manufacturer and a way to contact them.
5. Third-party testing, such as an NSF or USP mark. That is about quality control, not proof the product works.
6. No disease claims, and no "FDA approved".
7. A clear refund policy. It doesn't tell you whether the product works, but it tells you how the seller behaves.

And before any of that: get tested first, and talk to your doctor if you take medication. I cover the health side in my guide to side effects and who should skip boosters.

Frequently asked questions

Sources

1. US Food and Drug Administration. FDA 101: Dietary Supplements. fda.gov
2. US Food and Drug Administration. Avoiding products contaminated with hidden ingredients. fda.gov
3. Code of Federal Regulations, Title 21, section 101.36: Nutrition labeling of dietary supplements. ecfr.gov
4. Clemesha CG, Thaker H, Samplaski MK. "Testosterone boosting" supplements composition and claims are not supported by the academic literature. World J Mens Health. 2020:115-122.doi:10.5534/wjmh.190043
5. Tucker J, Fischer T, Upjohn L, Mazzera D, Kumar M. Unapproved pharmaceutical ingredients included in dietary supplements associated with US Food and Drug Administration warnings. JAMA Netw Open. 2018;1(6):e183337. doi:10.1001/jamanetworkopen.2018.3337

Marcus Hale
Writer at The Male Ledger. Not a doctor.

I write about testosterone, energy and vitality after 40, and I link to the studies so you can check my work. Marcus Hale is a pen name; here is why.