Phentermine vs Ritalin: Which is Better for Weight Loss?

January 10, 2024 |

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When thinking about weight loss pills, Phentermine is a common option that comes to mind. But lately, I have noticed many people talking about Ritalin and wondering if it’s worth trying.

Now, both Phentermine and Ritalin are amphetamines, but the usage of these drugs and their intended effects differ significantly.

Phentermine is FDA-approved for weight loss purposes (short-term only). It acts by stimulating the central nervous system to suppress appetite and is taken orally.

Whereas Ritalin is a stimulant used to treat ADHD and is NOT prescribed for weight loss except when used off-label since it decreases appetite.


Overall rating: 2.9/5
  • Suppresses hunger, gives energy, and enhances focus
  • FDA-approved for weight loss – Prescription only
  • FDA pregnancy category X
  • Highly likely to cause withdrawal symptoms
  • Contraindicated with other medications Metformin, SSRIs, MAOIs, etc


Overall rating: 2.3/5
  • Curbs appetite, energizes the body, and provides mental clarity
  • NOT FDA-approved for weight loss
  • FDA pregnacy category C
  • Unsafe for individuals with co-morbidities
  • Contraindicated with alcohol and other stimulants

What Is Phentermine & How Does it Work?

Phentermine is a sympathomimetic drug that mimics the activity of adrenaline and noradrenaline to stimulate the sympathetic nervous system. It is an FDA-approved weight loss aid that doctors typically prescribe to patients with a BMI of 30 or greater.

The combination of phentermine and exercise has been shown to be effective in helping people lose weight. Because of this, it helps to suppress appetite and increase metabolism which ultimately will help you shed the extra pounds.

Nonetheless, Phentermine shows a potential for abuse and may pose severe side effects; hence, it is a prescription-controlled drug.

Phentermine Pros

  • Blocks hunger, burns fat, and increases energy levels
  • Clinically proven efficacy
  • FDA-approved weight loss aid
  • Supports rapid weight loss

Phentermine Cons

  • FDA category X: unsafe in pregnancy
  • Not legal to use without a prescription
  • Caution is advised for prescription to elders
  • Short-term use
  • Sometimes poses severe health risks
  • Potential for abuse and dependence
  • Potential to give false-positive drug tests
  • Possible drug interactions.

What Is Ritalin & How Does it Work?

Ritalin is a prescription pill primarily used and FDA-approved for the treatment of ADHD and narcolepsy in pediatric patients aged between 6 to 12 years.

Nonetheless, it is used OFF-LABEL for supporting weight loss progress. 

It belongs to a family of drugs known as CNS stimulants and works on the central nervous system to suppress appetite and increase focus, making it easier to lose weight by keeping you from being distracted by hunger pangs or cravings for unhealthy foods. 

Ritalin Pros

  • Curbs hunger
  • Improves focus
  • Helps with weight unconventionally

Ritalin Cons

  • Not FDA approved as weight loss aid
  • Poses life-threatening and long-term side effects
  • Potential for abuse and dependence
  • Contraindicated with certain drugs

Differences Between Phentermine & Ritalin

Uses:Long-term treatment of ADHD – Prescription-only / CNS stimulantShort-term aid to weight loss – Prescription-only / CNS stimulant
Drug class:Central Nervous system stimulantsAnorexiants, CNS stimulants
Dosage:Available in 10mg tablets or capsules and is usually taken twice a day at least one hour before meals. The maximum daily dose is 40mg per day.Available in 5mg tablets or capsules and is usually taken once daily in the morning. The maximum daily dose is 60mg per day.
Side effects:Rare side effects. Dizziness or lightheadednessDry mouth, insomnia, constipation, diarrhea, and nervousness.
Dosage Form:Tablets and CapsulesExtended-release capsules allow for fewer doses
Drug interactions:Alcohol, other stimulantsMetformin, sibutramine, MAOIs, SSRIs, and benzodiazepines
Disease Interactions:Cardiac disease, Glaucoma, Hypertension, Liver diseases.Should be avoided by patients with heart disease or high blood pressure
Prescription requirement:Prescription-onlyPrescription-only under close medical supervision
Potential for Abuse:Less likely to cause withdrawal symptomsMore likely to cause symptoms of withdrawal
Pregnancy safety:Category C. Avoid if possibleCategory X; not safe for pregnancy

Phentermine vs. Ritalin – Product Comparison

Phentermine is a generic drug manufactured by multiple companies and sold under different trade names.

Two of its most popular brand names are Adipex-P and Lomaira. Among these, Lomaira is distributed by KVK tech which is a leading manufacturer for the American public.

In parallel, Adipex-P is produced by Sunrise Pharma, another well-known pharmaceutical company based in the United States. In comparison, Ritalin is the brand name of the active compound methylphenidate HCl manufactured by Novartis.

Key Ingredients 

Phentermine and Ritalin are based on a single active compound and are administered as a monotherapy.

Both of them work by stimulating the central nervous system, due to which you may feel a reduction in appetite, an increase in energy levels, and improved focus.

Common Ingredients

  • None

Ritalin Key Ingredients

  • Methylphenidate HCl

Phentermine Key Ingredients

  • Phentermine HCl

Dosage Regimen

The dosage regime of both phentermine and Ritalin varies depending on the person’s condition and their dose-response. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to.

Phentermine Dosage

The amount of phentermine that you take depends on the potency you’re prescribed.

Also, the number of doses you take each day, the time allowed between doses, and the length of time you take medicine depend on the medical problem for which you are using the medicine.

Nonetheless, phentermine offers four different dosage options. 

  • A 4 mg dose (which equals half a tablet) taken three times a day might provide ample relief from untimely cravings.
  • 15 or 30 mg capsules after a two-hour gap post-breakfast might be more appropriate.
  • An 18.75 mg dose (equaling half a tablet) once a day or taken orally twice daily. 
  • 37.5 mg capsules or tablets (Adipex-P) 1 to 2 hours after breakfast to achieve the desired impact.

Ritalin Dosage

Like phentermine, Ritalin also has numerous dosage regimes that the doctor adjusts according to the patient’s severity of ADHD.

  • The recommended Ritalin dosage for children with ADHD is 10 mg once daily after breakfast or lunch.
  • For those who weigh less than 77 pounds (35 kilograms), the dosage can be decreased to 2.5 milligrams (mg) daily.
  • For those who weigh between 77 and 113 pounds (35-51 kg), the dosage may be increased to 20 milligrams.

Also read: Adderall vs Phentermine: Which works better?


Both phentermine and Ritalin are based on a single active ingredient.

Your doctor can guide you better on the administration frequency and potency of both these pills because it varies depending on the health condition of every patient.

phenq cta2

Ritalin Vs. Phentermine – Which Is Best For Weight Loss?

Ritalin for Weight loss

  • Reduction Of Excess Fat

Ritalin has shown potential to induce fat loss. Correspondingly, a study performed on children taking methylphenidate showed that it leads to a significant reduction in fat mass, especially in abdominal fat.

  • Disrupts Appetite

Ritalin stimulates the production of dopamine and norepinephrine in your brain. These chemicals make you feel more alert, focused, and energetic and cause you to feel hungry less often. This reduction in your calorie intake while taking Ritalin may lead to weight loss.

This is evident from a study performed on obese men in which participants demonstrated a 23% decrease in energy intake with the moderate dose of methylphenidate (aka Ritalin) compared to the placebo.

Moreover, consuming the lowest effective dose of methylphenidate made the individuals consume 34% fewer kilocalories than the placebo.

In a nutshell, methylphenidate substantially reduced energy intake from highly palatable food by one-third in obese adult males. This effect may be attributed to the increased dopamine levels in the brain, as it plays an essential role in regulating hunger. On a side note, low dopamine levels in the brain may make you more hungry. 

Phentermine for Weight Loss

  • Eliminates Excess Fat

Phentermine works by increasing the levels of two chemicals called serotonin and norepinephrine in your brain.

Serotonin produces feelings of well-being and happiness, while norepinephrine boosts energy levels by helping you burn fat stores for fuel instead of carbohydrates from food.

  • Controls Binge eating

Phentermine triggers the release of norepinephrine in the central nervous system. The norepinephrine reduces hunger by activating the β-adrenergic receptors, which activate brain regions that control appetite.

Correspondingly, a 12-week clinical trial reported that the phentermine group lost 12.1% of their initial body weight, whereas the placebo group lost only 8.8%.

This weight reduction in both groups was attributed to reduced cravings for all food types, with the phentermine group showing a more significant decline in cravings for fats and sweets compared to the placebo.


Both drugs induce weight loss by a similar mechanism, but phentermine is the preferred supplement because it is backed by FDA approval.

Plus, Phentermine specifically targets excess weight, but Ritalin’s primary function is to treat ADHD or narcolepsy, and weight loss is only its side effect.

phenq cta2

Phentermine and Ritalin Side Effects – Which is Safer?

Phentermine Side Effects

Phentermine’s side effects may range from mild to severe to life-threatening.

  • Mild Side Effects

For instance, it may cause self-limiting gastrointestinal problems like nausea, abdominal pain, or changes in bowel movements.

  • Moderate Side Effects

The concerning side effects may include,

>> A fast/irregular/pounding heartbeat,

>> Mental/mood changes (such as irritability, uncontrolled anger, hallucinations, and anxiety) and changes in libido.

  • Severe Side Effects

Side effects that indicate an emergency include,

>> Severe allergic reaction to phentermine, trouble speaking, seizure, weakness on one side of the body, and vision changes (such as blurred vision).

Evidence from User Experience

phentermine review

Ritalin Side Effects

Ritalin’s side effects also vary in their range of severity.

  • Common Side Effects

The common side effects include,

>> Headache,

>>Emotional changes (aggression, irritability, depression, anxiety, tension),

>> Insomnia, loss of appetite leading to weight changes,

>> Stomach ache, dry mouth, and nausea or vomiting.

  • Serious Side Effects

Serious side effects encompass:

>> Mood or personality changes,

>> Suicidal thoughts or thoughts of harming others,

>> Irregular or rapid heartbeats (palpitations), high blood pressure,

>> Sudden onset of facial tics (involuntary muscle movements in the face),

>> Allergic reactions (anaphylaxis) to methylphenidate. 

  • Life-threatening side effects

Get immediate medical help if you feel you’re about to faint, have a seizure, have symptoms of a heart attack (such as chest/jaw/left arm pain, shortness of breath, unusual sweating), or have signs of a stroke (such as weakness on one side of the body, trouble speaking, sudden vision changes, confusion).

Evidence from User Experience

A Ritalin user documented her experience of taking Ritalin for ADHD and how it suppressed her appetite, but at what cost? Headaches, increased heart rate, cotton mouth, dizziness, loss of appetite, and a disturbed sleep pattern.


Both supplements have their fair share of side effects, which pose low to high risks to health, but phentermine is better among the two because of its clinically proven efficacy and approval by the FDA for weight loss.

However, in my opinion, when there are safer and better OTC alternatives available to such prescription drugs, you should try them before you opt for a weight loss pill like Phentermine.

phenq cta2

Can You Take Phentermine And Ritalin Together?

Phentermine and Ritalin together can be a dangerous combination. While these two drugs have similar effects on the body, they are very different in their chemical makeup, and combining them can cause serious side effects.

Phentermine is an appetite suppressant that works by increasing levels of norepinephrine in the brain.

Ritalin is a stimulant that works by increasing dopamine levels in the brain, which causes a feeling of euphoria and excitement.

Combining these two drugs can cause hyperactivity, insomnia, anxiety, restlessness, irritability, rapid heartbeat, tremors, and seizures. Additionally, there have been reports of people experiencing seizures while taking this drug combination.

How Long After Taking Phentermine Can I Take Ritalin?

You should never take phentermine and Ritalin together because both of them are CNS stimulants, and this may amplify their risk of causing side effects. 

So, what is the best way to adjust their dosage regimes?

Well, Phentermine stays in your system for approximately FOUR DAYS; therefore, to be on the safe side, you should take Ritalin for at least five to six days. This ensures that phentermine has been flushed out of your system and rules out potential drug interactions.

Phentermine And Ritalin Interactions

If you are considering taking Phentermine or Ritalin, you should be aware of the potential interactions between it and other drugs.

For example, a medication for diabetes may interact with another medication, such as phentermine or Ritalin, to lower blood sugar levels too much. It can be dangerous if it causes dizziness, weakness, and fainting. It can also lead to severe hypoglycemia (low blood sugar).

Phentermine Drug Interactions

The following are some of the most commonly prescribed medications that interact with phentermine:

  • Antidepressants: Tricyclic antidepressants such as amitriptyline (Elavil), imipramine (Tofranil), desipramine (Norpramin), nortriptyline (Aventyl), protriptyline (Pamelor) and selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac), paroxetine (Paxil) and sertraline (Zoloft). May increase the risk of development of certain conditions like serotonin syndrome.
  • Antihistamines: Promethazine and diphenhydramine. Phentermine may decrease the sedative activities of these drugs.
  • Antibiotics: Tetracyclines, erythromycin, chloramphenicol, quinolones, and sulfonamides. These antibiotics may decrease the metabolism of phentermine.
  • Alcohol: Alcohol interferes with the metabolism of phentermine.
  • Central nervous system depressants: barbiturates, benzodiazepines. This combination amplifies the risk of the onset of depression.

Ritalin Drug interactions

The following are some of the most commonly prescribed medications that interact with Ritalin:

  • Antidepressants: Tricyclic antidepressants such as amitriptyline (Elavil), imipramine (Tofranil), desipramine (Norpramin), nortriptyline (Aventyl), protriptyline (Pamelor) and doxepin (Sinequan). These can increase the risk of side effects. If you are taking one of these medications, consult your physician before taking Ritalin.
  • Narcotic analgesics: Examples include codeine, hydrocodone, meperidine, morphine and oxycodone. These drugs can cause drowsiness, confusion, and dizziness when taken together with Ritalin. If you take narcotic pain relievers for any reason, be sure to consult your physician before taking Ritalin.
  • Antihistamines: An example is diphenhydramine (Benadryl). This drug may cause drowsiness when taken together with Ritalin.
  • Barbiturates: Barbiturates such as phenobarbital or secobarbital. Ritalin may increase the sedative effects of these drugs, which can cause drowsiness and dizziness.
  • Inhibitors of Cytochrome P450 2D6: selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac) and paroxetine (Paxil). Serotonin-norepinephrine reuptake inhibitors (SNRIs) such as venlafaxine (Effexor) may also inhibit the metabolism of Ritalin.

Ritalin vs. Phentermine Alternatives & Substitutes

Choosing a weight loss solution can be confusing and overwhelming. Ritalin and Phentermine are two common options for weight loss, but both have the potential for misuse and dependence, and any weight you lose may come back when you stop taking them.

In this case, PhenQ is a suitable over-the-counter alternative to both these prescription diet pills. It is an all-natural supplement that helps with weight loss without the side effects of Ritalin or Phentermine.

It helps burn fat faster while suppressing your appetite. It also helps boost your metabolism to burn more calories throughout the day.


How many calories does Ritalin burn?

According to real user experience, Ritalin may help you lose 3 to 4 pounds per week.

How long does it take to lose weight on Ritalin?

You may start seeing a reduction in your pounds within the first week. Nonetheless, it may take at least a month to bring a noticeable difference in your physique.

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