The Possible Risks and Side Effects of Stacker Brand Diet Pills
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The Possible Risks and Side Effects of Stacker Brand Diet Pills

The Possible Risks and Side Effects of Stacker Brand Diet Pills
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Updated on November 14, 2025
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Each year, millions of people turn to diet pills to lose weight. As of 2022, about 15 percent of U.S. adults reported using a weight-loss supplement at some point in their lives.

One popular over-the-counter diet supplement brand is Stacker. The supplements (in the form of pills and gummies) come in a few versions — Stacker, Stacker 2, and Stacker 3 — each with different formulations.

While many people use Stacker diet pills, there is not enough evidence to show that they can help you lose weight safely or healthily. On top of that, taking Stacker pills can come with potential risks and side effects.

Here, learn how effective Stacker diet pills are, as well as the potential side effects and risks of taking these supplements.

Talk to your doctor before trying any weight-loss supplement, as they may not be safe or appropriate for your needs.

What Are Stacker Diet Pills Made Of?

Each Stacker formulation has different herbal ingredients, including sources of caffeine, all purported to aid in fat burning and weight loss.

Some main ingredients in Stacker 2 and Stacker 3 products include the following:

  • Kola nut: A source of caffeine that's used as a stimulant.
  • Yerba mate: A traditional herbal tea with caffeine. Some studies suggest that it may affect weight loss.
  • White willow bark: An herb that has been traditionally used to relieve pain and reduce inflammation in the body.
  • L-alanine: A non-essential amino acid that is involved in sugar and acid metabolism and provides energy to muscle tissue.
  • Taurine: An amino acid found in many proteins like meat and fish. It helps give the brain and body more energy, and is often found in energy drinks.

  • Green tea leaf extract: A source of caffeine that can boost energy.
  • Yohimbe: A bark extract that is claimed to enhance male sexual performance, promote weight loss, and help diabetic neuropathy. There is a standardized prescription drug form in the U.S., however, the herb itself has been on the U.S. Food and Drug Administration (FDA) list of unsafe herbs since 1997, due to its side effects. It's also banned in several countries.

  • Chitosan: An extract from the shells of sea creatures. Marketers who promote chitosan for weight loss claim it binds to fat and cholesterol to prevent their absorption in the body. But studies have found that chitosan does not increase the level of fat excreted.

How Effective Are Stacker Diet Pills?

Stacker's website claims that the diet pills work to help suppress your appetite, boost your metabolism, and help you burn fat. But there is not enough evidence to sufficiently verify any of these claims, and most of the ingredients do not have enough strong research behind them to show that they significantly reduce body fat or weight.

The only ingredient with sufficient research related to weight loss is caffeine. Caffeine intake may help promote weight, BMI, and body fat reduction.

This effect, however, is often only short-term. No conclusive studies have been able to determine the long-term effect of caffeine on weight loss.

Are Stacker Diet Pills FDA Regulated?

Before using Stacker diet pills, be aware that the FDA does not regulate supplements for weight loss. Just like other dietary supplements (including vitamins), pre-market review or approval by the FDA is not required. This means dosages listed on the labels of diet pills like Stacker could be inaccurate, and each batch of pills could vary greatly in the amount of ingredients they contain.

The FDA will ban certain ingredients from diet pills, however, if they are deemed harmful. One example is ephedra, which was banned for use in weight-loss supplements in 2004. (Stacker diet pills used to contain ephedra, but they do not anymore, according to the company's website.)

If an ingredient has been reported to cause adverse effects enough times, the FDA will consider prohibiting its sale.

Side Effects of Stacker Diet Pills

Taking Stacker diet pills (or any weight-loss pills) can come with a range of potential side effects.

1. Caffeine Toxicity

Because of their high caffeine content, herbal diet pills like Stacker 2 and 3 may cause nervousness, shaking, headaches, and dizziness.

Too much caffeine can also sometimes lead to caffeine toxicity, with symptoms like restlessness, anxiety, arrhythmias, nausea, vomiting, and electrolyte imbalance.

It's hard to determine just how much caffeine is in each Stacker product because the amount often isn't clearly listed on the label. But most contain somewhere in the neighborhood of 200 to 400 mg (milligrams) of caffeine, which is the equivalent of about two to five 8-ounce cups of coffee. This is generally considered a safe amount for healthy adults.

That amount may not bother everyone, but it can have negative side effects for those who are more sensitive to caffeine — and it may be too much if you're getting additional caffeine from coffee, tea, soda, or other sources of caffeine. Pregnant people, children, and people with a chronic health condition should check with their doctor for advice on how much caffeine they can consume safely.

2. Digestive Issues

Prescription and over-the-counter weight-loss supplements can also cause digestive issues like constipation and diarrhea.

Chitosan can cause constipation, gas, and abdominal cramping when taken in large amounts. You should also not take chitosan if you're allergic to shellfish.

3. Drug Interactions

Lastly, the herbs in Stacker diet pills may negatively interact with any prescription or over-the-counter medications you're taking. For example, white willow bark is a known blood thinner, which could be unsafe for people on blood thinner medications or those dealing with heart issues.

Possible Long-Term Risks of Stacker Diet Pills

Ingredients in diet pills can lead to long-term risks and side effects, including:

1. High Blood Pressure

Stacker diet pills contain high doses of caffeine, which can also increase blood pressure (especially if you already deal with hypertension).

Yohimbine, a component of yohimbe, has been associated with high blood pressure.

2. Cardiac Issues

There is little to no research surrounding Stacker 2 and 3's influence on cardiovascular health, in particular. But there is some research around its specific ingredients, including yohimbe, which has been associated with heart attacks, seizures, and a dangerously high heart rate (tachycardia).

3. Psychological Effects

Stacker diet pills can produce a variety of psychological side effects because of their caffeine content. Too much caffeine every day can cause symptoms like insomnia, restlessness, and anxiety.

Similarly, the ingredient yohimbe has been found to cause anxiety issues.

The Takeaway

  • Stacker is a brand of over-the-counter supplement intended to help with weight loss; its main ingredients are caffeine and an assortment of herbs, such as willow bark and yohimbe.
  • While there are some ingredients associated with ‌short-term‌ weight loss, like caffeine, there is not enough evidence to show that the combined ingredients in Stacker pills will help you safely lose weight, if at all.
  • Stacker diet pills can also come with a number of side effects due to their caffeine content and herbal combinations. Some ingredients can even pose serious health risks.
  • Talk to your doctor before trying any weight-loss supplement to make sure that it is safe and healthy for you.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Dietary Supplements for Weight Loss. National Institutes of Health Office of Dietary Supplements. May 8, 2022.
  2. Taurine is an ingredient in energy drinks Is taurine safe? Mayo Clinic. May 10, 2023.
  3. Yohimbe. National Center for Complementary and Integrative Health. May 2025.
  4. Chitosan. Memorial Sloan Kettering Cancer Center. March 29, 2022.
  5. Gutiérrez-Hellín J et al. Research Trends in the Effect of Caffeine Intake on Fat Oxidation: A Bibliometric and Visual Analysis. Nutrients. October 10, 2023.
  6. What’s in your supplement? Harvard Health Publishing. February 15, 2019.
  7. Caffeine. National Library of Medicine Medline Plus.
  8. Murray A et al. Caffeine Toxicity. StatPearls. February 6, 2025.
  9. Coffee. Harvard T.H. Chan School of Public Health Nutrition Source. July 2020.
  10. Willow Bark. Memorial Sloan Kettering Cancer Center. Decemeber 17, 2021.
  11. Meamar M et al. Chapter Six - Coffee and mental disorders: How caffeine affects anxiety and depression. Progress in Brain Research. 2024.
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Sean Hashmi, MD

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Castle Connolly Top Doctor, Member of American College of Lifestyle Medicine

Sean Hashmi, MD, is an experienced nephrologist and obesity medicine specialist based in Southern California. As the regional director for clinical nutrition and weight management at a prominent healthcare organization in Southern California, Dr. Hashmi oversees the development and implementation of cutting-edge nutritional programs and weight management strategies. With his innovative approach and unwavering commitment to providing evidence-based solutions, he is a highly sought-after speaker and a leader in his field.

Hashmi founded the nonprofit organization SelfPrinciple.org to provide accessible and accurate health, nutrition, and wellness information to the public. Through this platform, he shares the latest research findings, empowering individuals to make informed decisions about their well-being. Self Principle also supports children's education by providing scholarships, books, and supplies, so that students have the resources necessary to succeed academically and build a brighter future.

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