The Possible Risks and Side Effects of Stacker Brand Diet Pills

Stacker brand diet pills can cause caffeine toxicity, among other side effects.
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Each year, millions of people turn to diet pills in an effort to lose weight. In fact, as of 2022, about 15 percent of U.S. adults have used a weight-loss supplement at some point in their lives, per the National Institutes of Health (NIH).


Some people will use diet pills on top of other weight-loss efforts like diet and exercise, while others believe the pills alone will substitute natural efforts.

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One popular over-the-counter diet supplement brand is Stacker, which has been marketed by many celebrities throughout the years.

Since 1997, Stacker diet pills have been produced by the company NVE Pharmaceuticals, based in New Jersey, and have been sold to people who want to lose weight quickly, per Stacker's website. The supplements (in the form of pills) also 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 along with the 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, per Mount Sinai.
  • Yerba mate:‌ A traditional herbal tea with caffeine. Some studies suggest that it may affect weight loss, per the Mayo Clinic.
  • White willow bark:‌ An herb that has been traditionally used to relieve pain and reduce inflammation in the body, per Mount Sinai.
  • L-alanine:‌ A non-essential amino acid that is involved in sugar and acid metabolism and provides energy to muscle tissue, per the National Library of Medicine (NLM).
  • 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, per the Mayo Clinic.
  • Green tea leaf extract:‌ A source of caffeine that can boost energy, per the Cleveland Clinic.
  • Yohimbe:‌ A bark extract that is claimed to enhance male sexual performance, promote weight loss and help diabetic neuropathy, per the NIH. There is a standardized prescription drug form in the U.S., however, the herb itself has been on the FDA's list of unsafe herbs since 1997, due to its side effects, per Kaiser Permanente. It's also banned in several countries, per the NIH.
  • Chitosan:‌ An extract from the shells of sea creatures. Marketers that 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, per the Memorial Sloan Kettering Cancer Center (MSKCC).



Some of these ingredients may sound unfamiliar, but many of them are included in supplements that claim to promote fat and weight loss.

Each Stacker dose contains about 200 milligrams of caffeine (like many other diet pills), per the NIH.

How Effective Are Stacker Diet Pills?

Stacker's website claims that Stacker diet pills will work to help suppress your appetite, boost your metabolism and help you burn fat. There are also customer and celebrity claims that Stacker diet pills work for quick weight loss.


But there is not enough evidence to sufficiently verify any these claims.

And most of the ingredients do not have enough strong research to show that they significantly reduce body fat and/or weight.

For example, the ingredient chitosan has been studied in the past, but the results have often shown that it does not significantly aid weight loss or keep fat from binding to your body, per New York University's Department of Surgery. There have not been any recent studies on the ingredient, yet NVE Pharmaceuticals still includes chitosan in Stacker 3 products.


The only ingredient with sufficient research related to weight loss is caffeine. In fact, according to one October 2018 meta-analysis in Critical Reviews in Food Science and Nutrition,‌ 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, according to the Obesity Action Coalition.



Ultimately, Stacker diet pills are not effective at helping people lose weight in a long-term or healthy way. If you are losing weight while on these pills, it's most likely due to your lifestyle changes (diet and exercise) versus the pills themselves.

Are Stacker Diet Pills FDA Regulated?

Before using Stacker diet pills, beware that the U.S. Food and Drug Administration (FDA) does not regulate supplements for weight loss. Just like other dietary supplements (including vitamins), premarket review or approval by the FDA is not required, according to Penn Medicine.


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, per Harvard Health Publishing.


One good thing, however, is that the FDA will ban certain ingredients from diet pills if deemed too harmful — like the plant ephedra, which was banned for use in weight-loss supplements in 2004. (Stacker diet pills used to contain ephedra, but they do not any more, per the company's website.) A form of ephedra — ephedrine — is still used in small amounts in some decongestants, per the Mayo Clinic.

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

Side Effects of Stacker Diet Pills

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

1. Caffeine Toxicity

First, because of their high caffeine content, herbal diet pills like Stacker 2 and 3 may cause nervousness, shaking, headaches and dizziness, per the NLM.

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

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 milligrams of caffeine, which is the equivalent of about two to four eight-ounce cups of coffee.

That amount may not bother certain people, 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.


2. Digestive Issues

Prescription and over-the-counter weight-loss supplements can also cause digestive issues like constipation and diarrhea, which can lead to dehydration if left untreated, per the Mayo Clinic.

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, per the MSKCC.

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, per the NLM.

Always talk with your doctor before trying any diet supplement.

How Much Caffeine Is Safe to Consume per Day?

Up to 400 milligrams of caffeine per day seems to be safe for most healthy adults. Anything above that can cause potentially harmful side effects like fast heartbeat and muscle tremors, and it can negatively interact with substances like alcohol and other prescription medications, per the Mayo Clinic. This is why it's important to not take an excess amount of weight-loss pills that contain caffeine.

If you're unsure about how much of a diet pill you can take, talk to your doctor, who can offer some guidance.

3 Possible Long-Term Risks of Stacker Diet Pills

While there are risks with all versions of Stacker diet pills, the original version that contained ephedra might pose a higher risk, as the ingredient was banned by the FDA for its dangerous side effects.

That said, other ingredients in the diet pills can lead to long-term risks and side effects, including the following:

1. High Blood Pressure

The original version of Stacker diet pills contained ephedra — or ephedrine — which mimics the production of adrenaline in the human body, per the NLM. But as we've learned, newer iterations (like Stacker 2 and 3) are ephedra-free.

One of the reasons ephedra was banned was because it increases blood pressure, which can lead to heart disease, stroke, kidney issues and even cognitive issues, per the NLM.


Besides that, Stacker diet pills still contain high doses of caffeine, which can also increase blood pressure (especially if you already deal with hypertension), per the Mayo Clinic.

The ingredient yohimbe has also been known to increase blood pressure, per the NIH.

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.

Per the NIH, the ingredient yohimbe in Stacker 3 has been associated with heart attacks, seizures and a dangerously high heart rate (tachycardia).

As we've noted, older Stacker formulations contained ephedra, which has since been banned. Older research on ephedra, including a March 2004 review in the ‌Annals of Pharmacotherapy,‌ found it was associated with adverse heart issues like myocarditis (enlargement of the heart), arrhythmias (irregular heart beat) and even cardiac arrest.

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, anxiety, fear and agitation, per the American Psychological Association.

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

The original version of Stacker diet pills, which contained a caffeine and ephedra combination, had the potential to create insomnia in users, which only exacerbates psychological symptoms, per New York University's Department of Surgery.

The Bottom Line

Just because a diet pill is on the market and supported by celebrities does not mean it's safe and healthy for you.

There is not enough research to show that Stacker diet pills are effective at causing healthy and sustainable weight loss. 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.

On top of that, Stacker diet pills (whether the original version, Stacker 2 or Stacker 3) can come with a number of side effects due to their caffeine content and herbal combinations. Some ingredients can even pose serious health risks.

Ultimately, you should talk to your doctor before trying any weight-loss supplement to make sure that it is safe and healthy for you.




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