Side Effects of Weight Loss Pills and Supplements

Do you have serious health issues as a result of your weight? Are you trying diet and exercise but not losing enough weight? You may be interested in weight loss pills if you answered yes to these questions.

It’s important to know, however, that weight loss supplements are used in conjunction with diet and exercise, not instead of them.

Diet pills claim to help you lose weight, or at least make it easier if you combine them with other methods.

Most of them use one or more of these mechanisms:

  • Reducing appetite, so you feel fuller and eat fewer calories
  • Reduce absorption of nutrients such as fat, resulting in fewer calories
  • Increasing fat burning makes you burn more calories

What Are Diet Supplements?

Diet supplements are products you take orally that are intended to add to your normal diet. A supplement does not have to promote weight loss; it may provide an important nutritional replacement for consumers who don’t get enough of a particular ingredient in their diets. 

A dietary supplement may contain:

  • Vitamins
  • Minerals
  • Enzymes
  • Amino acids (Building blocks of protein)
  • Glandular extracts
  • Botanical products/herbs
  • Organ products

People take diet supplements for a variety of reasons: to lose or gain weight, to build muscle tissue, to improve sleep, to boost energy, to restore lost nutrients.

A diet pill or supplement sold at a local drugstore or through an online retailer in attractive packaging does not guarantee its safety. 

Before dietary supplements are marketed, the FDA is not authorized to review them for safety and effectiveness. Manufacturers and distributors of dietary supplements are responsible for ensuring the safety of their products.

There are three basic types of diet pills, based on their chemical composition and how they affect the body. These types of diet pills include:

  • Stimulant – Increases energy and a sense of well-being by affecting the central nervous system. Stimulants can also reduce appetite.
  • Appetite-suppressant – The effects increase feelings of fullness and reduce appetite by increasing serotonin and norepinephrine neurotransmitters in the brain.
  • Fat Inhibitor – Acts in the gastrointestinal tract (i.e. stomach and intestines) to reduce fat absorption by a third.

There are certain formulations of diet pills approved by the FDA, though not all. A prescription weight loss aid is typically prescribed to patients who have a body mass index (BMI) over 30, or who have a BMI of at least 27 and a disorder that may be adversely affected by weight (such as Type 2 Diabetes). Misuse or abuse of these medications can be fatal.

I have also reviewed a lot of other weight loss supplements, if you are interested, you might check them out.

How Do Weight Loss Supplements Work?

No matter what kind of dietary supplement you’re looking for, you’ll have plenty of options. According to the companies that distribute these products, the ingredients in their supplements can help you achieve the following results:

  • Eat less food (chickweed, pollen, fennel)
  • Prevents you from overeating (guar gum, psyllium)
  • Boost your metabolism (caffeine, guarana, synephrine, B-complex vitamins)
  • Reduce fat production (green tea, hydro citric acid, flaxseed)
  • Prevents your body from absorbing fats from your food (chondroitin)

From pills and capsules to powders, liquids, and teas, diet supplements are available in just about any form you can take orally. It is possible to take some products along with a meal, while others can be taken instead. 

When patients have a body mass index (BMI) of 27 or higher, doctors sometimes recommend prescription weight loss pills, in combination with diet and exercise. Diet pills and supplements can be purchased over the counter without a prescription.

You lose weight by stimulating your metabolism, which is your body’s method of using energy, with over-the-counter diet pills. 

Caffeine is a central nervous stimulant found in products like Dexatrim with Metabolic Support that may help you burn fat through a process called thermogenesis. However, taking these stimulants can have serious side effects.

These products can even cause serious health problems, such as liver damage or heart problems. If you buy an over-the-counter medicine or supplement, you should always seek your GP’s approval before taking it.

Risks and Side Effects of Weight Loss Pills

Even though social media has made certain weight loss supplements popular, these unverified and unstudied medications can be dangerous. As with other over-the-counter drugs, “herbal” weight loss pills are not approved by the FDA as safe methods for losing weight. 

It is important to be suspicious of any pills that promise significant weight loss in a short period of time – these can cause serious side effects or simply not work.

Clinical trials are likely to have been conducted on approved drugs from registered sellers prior to release to the market. The reality is that even tested and approved diet pills can come with unpleasant side effects and risks. 

Some of these pills come with unclear long-term effects, while others are approved for sale only to be withdrawn after a potential health risk is identified. 

There are also health risks associated with buying weight loss pills online. 

According to the Medicines and Healthcare products Regulatory Agency (MHRA), one in ten UK residents has bought fake medical products online in the past year. MHRA also found that 63% of people who took slimming pills they bought online experienced unpleasant side effects, including diarrhoea, bleeding, blurred vision, and heart problems.

Many diet supplements are harmless, and some may even be effective at boosting your metabolism, burning fat, or creating a sense of fullness. In spite of this, some of the most popular ingredients in weight loss products have been banned by the FDA, such as:

  • Sleeplessness
  • Increased heart rate
  • Diarrhoea
  • High blood pressure
  • Agitation
  • Liver damage
  • Kidney problems
  • Ephedra – Banned
  • Rectal bleeding

Chinese herbal stimulant ephedra was once widely sold in diet supplements but was banned in 2004 after studies discovered it may increase the risk of heart attacks and strokes. Lower courts ruled in 2005 that ephedra can be used in small doses. A federal appeals court reinstated the FDA’s ban on ephedra in 2006, ruling that it was too dangerous for use as a supplement.

Hydroxycut – Recalled and Banned

The kidneys, liver, and other vital organs can be severely damaged by weight loss products. Hydroxycut products were banned and recalled in 2009 due to severe adverse reactions, including jaundice and hepatitis. The supplements led to the death of one person and the need for a liver transplant in another.

Fen-Phen – Recalled

The off-label diet drug Fen-Phen included the active ingredient Fenfluramine, which was recalled in the late 1990s after it was linked to heart damage and lung disease. Phentermine, another primary ingredient of Fen-Phen, is still prescribed in some cases for weight loss, but only with a doctor’s prescription.

Meridia – Withdrawn from the Market

In 2010, Meridia, a prescription drug sold under the name Sibutramine, was withdrawn from the market after a clinical study indicated that the drug may increase the risk of heart attack or stroke. Sibutramine was originally prescribed as an appetite suppressant and weight management drug, according to the National Institutes of Health. Meridia was linked to evidence of cardiovascular damage, which led the manufacturer to voluntarily stop production.

Effects of Weight Loss Pill Abuse

Stimulants pose a high dependency risk as a category of diet pills. Like other stimulants like cocaine, amphetamines affect systems in the brain responsible for feelings of happiness or contentment. 

Furthermore, many people develop a tolerance to the energy they receive from their pills and eventually take more. These are common signs of addiction.

A stimulant-type diet pill’s short-term effects include a rush of energy, increased blood pressure, dizziness, and flushed skin. Taking these pills regularly may cause insomnia, constipation, hypertension, and heart valve diseases as well as withdrawal symptoms if the person stops taking them. 

It is common for appetite suppressants to cause headaches, dizziness, and digestive problems. The same applies to fat inhibitors, which are known to cause unpleasant symptoms such as oily spotting, gas, and similar digestive problems.

How To Get Good Quality Weight Loss Supplements?

Manufacturers and distributors of dietary supplements must include their name and location on labels.

Check with the manufacturer or distributor if you want to know more about the product you are taking:

  • Supporting information for the product’s claims
  • Information on the safety and effectiveness of the product’s ingredients.

Become a savvy supplement user. To do so, follow these steps:

  • Instead of relying on information provided by sellers when searching the internet for supplements, you should use noncommercial sites (e.g. NIH, FDA, USDA).
  • If a claim sounds too good to be true, it probably is. Be wary of product claims such as “works better than [a prescription drug]” or “has no side effects.”
  • It’s important to know that natural ingredients don’t always equate to safe.
  • You should consult your healthcare provider before taking a supplement.

“Good manufacturing practices” (GMPs) require manufacturers to follow a set of quality standards for their supplements. It has been found that some products contain more or less of the ingredient than stated on the label. They may also contain ingredients that aren’t listed on the label, such as prescription drugs.

Alternatively, you can contact the manufacturer to ask what research they’ve done to confirm the supplement’s benefits, what production standards they use, and what side effects have been reported. The FDA’s website can help you determine whether the supplement has been recalled.

These ingredients were not listed on the product labels, so consumers would not be aware that they were ingesting them:

  • Sibutramine: Weight-loss drug withdrawn from the market because of its association with high blood pressure, heart attacks, and strokes
  • Rimonabant: FDA does not approve the use of this appetite suppressant
  • Phenytoin: Anti-seizure medication
  • Phenolphthalein: Cancer-causing experimental drug

Consumers have been warned not to purchase supplements on the FDA’s list of tainted products, but this agency cannot test every product on the market. Any weight loss supplement should be taken under the supervision of a healthcare professional.

What drugs are approved for weight loss?

The US Food and Drug Administration has approved four weight-loss drugs for long-term use:

  • Bupropion-naltrexone (Contrave)
  • Liraglutide (Saxenda)
  • Orlistat (Xenical)
  • Phentermine-topiramate (Qsymia)

Most prescription weight-loss drugs work by reducing appetite or increasing feelings of fullness. Some work both ways. Orlistat is an exception. It interferes with fat absorption.


A combination of bupropion and naltrexone is called bupropion-naltrexone. This drug is used to treat addiction to alcohol and opioids. Antidepressant and quit-smoking aid, bupropion is a prescription medication. 

All antidepressants carry warnings about suicide risk, including bupropion. When starting this treatment, blood pressure should be monitored because bupropion-naltrexone can raise it. Constipation, headaches, and nausea are common side effects.


Diabetes can also be managed with liraglutide. Liraglutide is administered via injection, unlike other weight-loss drugs. Patients often complain of nausea. This may limit the effectiveness of the drug.


Reduced-strength forms of Orlistat are also available without a prescription (Alli). It can cause unpleasant gastrointestinal side effects, such as diarrhoea and flatulence. When taking this medication, you should follow a low-fat diet. Serious liver damage has been reported with orlistat. However, no causal link has been established.


In phentermine-topiramate, a weight-loss drug (phentermine) is combined with an anticonvulsant (topiramate). Since phentermine acts as amphetamine, it can be abused. An increase in heart rate and blood pressure may also occur, as well as insomnia, constipation, and nervousness. The drug increases the risk of birth defects.

Weight loss can also be achieved with phentermine on its own (Adipex-P, Lomaira). This is one of four similar weight-loss drugs approved for short-term use (less than 12 weeks). None of the other drugs in this group are widely prescribed.

Should You Take Weight Loss Pills?

The answer to weight loss isn’t as simple as pills. However, they may help you improve your health and lose weight by making the necessary changes to your lifestyle.

Weight loss pills, however effective, can’t address psychological issues that contribute to a person’s weight. 

There is no quick fix for weight gain, it requires a deep dive into what contributed to weight gain in the first place – environment, psychosocial factors, level of physical activity, history of disordered eating patterns, food history, exposure to nutrition education, genetic factors, and much more.

Taking diet pills should also be considered along with the possible side effects and drug interactions. You should also keep in mind that certain people should never take diet pills. 

If you are pregnant or breastfeeding, have a history of disordered eating, have diabetes, or are taking medication for hyperglycemia, you should avoid it.

Weight loss pills or supplements can’t work alone, they have to work in conjunction with everything else you do throughout the day.

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