What Is the Most Effective Weight Loss Pill? 6 Prescription Drugs

1. Phentermine/topiramate (Qsymia)

Qsymia works by suppressing your appetite, making you feel full, and increasing your metabolic rate. It is a combination of phentermine and topiramate, a seizure and migraine medication and is safe to use for long periods of time.

Side effects may include tingling in the hands and feet, disorientation, altered sense of taste, sleeplessness, diarrhea, and dry mouth. Complications include certain birth deformities (cleft lip and palate), fast heart rate, suicidal thoughts or behaviors, and eye problems that could lead to irreversible vision loss if left untreated.

Women who are pregnant or planning to get pregnant should take a pregnancy test before starting Qsymia and continue to use birth control while on the medication. If you have glaucoma, hyperthyroidism, heart disease or stroke, you should not take Qsymia. When you first start taking the medicine or increase dosages, get your heart checked regularly.

2. Phentermine (Adipex-P)

Phentermine also works by suppressing your appetite. It is only approved to be taken for a limited period (a few weeks). 

Side effects may include high blood pressure, heart palpitations, restlessness, disorientation, tremor, sleeplessness, shortness of breath, chest pain, dry mouth, bad taste, diarrhea, constipation, and vomiting. It's best to avoid taking it late at night because it can cause sleeplessness.

There is a risk of becoming addicted to this medication. If you take insulin for diabetes, tell your doctor before starting phentermine because your insulin dose may need to be adjusted. Avoid using phentermine if you have a history of heart disease, stroke, congestive heart failure, or uncontrolled high blood pressure, you should avoid using phentermine. Do not take the pill if you have glaucoma, hyperthyroidism, a history of drug misuse, or if you are pregnant or nursing.

3. Orlistat (Alli)

Orlistat is a weight loss pill that helps you lose weight by preventing about one-third of the fat you eat from being absorbed by your body. It is safe for long-term use. 

Possible side effects include abdominal discomfort, flatulence, leaking greasy feces, and inability to regulate bowel movements. These side effects are usually minor and only last a short time. Eating high-fat foods can worsen these effects. Rare occurrences of serious liver injury have been observed in people who use orlistat, although it is unclear whether the medication is to blame. 

Before taking orlistat, you should be on a low-fat diet, with less than 30% of your daily calories coming from fat. Moreover, you should take a multivitamin at least 2 hours before or after taking orlistat because the drug makes it difficult for your body to absorb vitamins A, D, E, and K for a short period of time. 

4. Liraglutide (Saxenda)

Liraglutide is a type II diabetes medication that works by simulating an intestinal hormone that alerts your brain when your stomach is full. It is safe for long-term use. 

Side effects include nausea, vomiting, diarrhea, constipation, low blood pressure, and increased hunger. Serious side effects include raised heart rate, pancreatitis, gallbladder disease, kidney disorder, and suicidal thoughts. 

Liraglutide has been shown to cause thyroid tumors in animals in studies. However, it is unknown whether it can cause thyroid cancer in humans. If you don't lose 4% of your body weight 16 weeks after being on liraglutide, your doctor may advise you to stop taking it because it may not work for you.

5. Bupropion and naltrexone HCl (Contrave)

Contrave is a formulation of two FDA-approved medicines, naltrexone and bupropion. Naltrexone is a drug that is used to treat alcohol and opiate addiction. Bupropion is a medication that is used to treat depression and seasonal affective disorder and to aid in the cessation of smoking. It is safe for long-term use.  

Common side effects include nausea, constipation, headache, vomiting, dizziness, sleeplessness, dry mouth, raised blood pressure, and increased heart rate. According to drug warnings, bupropion is associated with an elevated risk of suicidal thoughts and behaviors as well as significant neuropsychiatric disorders. Contrave can cause seizures and should not be used if you have a seizure disorder. 

6. Semaglutide (Wegovy)

Semaglutide works by replicating a hormone that promotes insulin production and suppresses hunger. Semaglutide was first approved for the treatment of type II diabetes, and it is safe for long-term use. 

Side effects are typically minor and may include abdominal cramping, constipation, vomiting, passing gas, headache, fatigue, and gastroesophageal reflux. Rare complications may include problems with kidney function and cloudy vision. 

Semaglutide use has been linked to pancreatitis. If you notice signs of pancreatitis, such as severe abdominal pain or nausea and vomiting that won't stop, seek medical attention right away.