Phentermine 37.5 mg vs. 30 Mg: Why You Should Care About Your Dose

If you’ve done your research very well, you’d have noticed phentermine HCL a lot, and a whole lot of other information – including its various doses. Since it’s an appetite suppressant, you’ll probably want to know if there’s a difference between these doses, and why your doctor prescribed phentermine 37.5 mg instead of the 30 mg dose. 

To really understand why there are different doses though, you’ll actually need to start at the very heart of how this drug works in your body. So you’ll be seeing the merits first, then what these differences in dosage mean, in the last part of the article. Let’s get started. 

Advantages of Phentermine – How It Works 

The summary of the advantages of phentermine is simply that; 

  • It suppresses appetite 
  • It speeds up your energy consumption rate 

Now for the more complicated answer, let’s see how it actually does this. 

A single dose of phentermine, once taken stimulates your central nervous system to secrete some hormones – one of the hormones tricks your brain into believing it isn’t hungry while another triggers an adrenalin rush. 

When your hunger pangs are suppressed, you won’t feel the need to eat as much as you used to, so you won’t be gaining additional weight once you’ve started your weight loss journey. 

The adrenaline rush triggered is a little more complicated, but here’s the simplified version. 

In a situation where you’re connered, your body decides whether to stay and confront the danger or to get as far away from the danger as possible. Either way, your adrenaline goes into action and prepares your body to act in ways you may not be able to under normal circumstances. 

For example, that Malian immigrant (now a French citizen) who climbed a ton of balconies to save a baby probably wouldn’t have had the strength to climb those same balconies on a normal day. He was able to do this because all he wanted was to make sure the baby was saved, and his body did what it needed to do. 

Note that he will also have expended a lot of energy – which his body would have found a way to provide (even if it meant burning fat reserves and muscles). 

The point here is that when you take a phentermine 37.5 mg tablet, your body forces your adrenaline rush. So you’ll basically be expending a lot of energy even while your appetite is suppressed and you’re not eating anything. It will dig through whatever reserves you have and find the energy needed to stay alert. 

That’s how you end up losing a ton of weight just from a pill. 

The downside to an artificially induced adrenaline rush is that you get all the symptoms – including a racing heart rate and high blood pressure. It’s because of these adverse symptoms that there are different doses of the tablet. Let’s move on to how the doses differ. 

Phentermine 37.5 mg VS 30 mg 

There are many advantages of phentermine, and one of them is that it can be administered in different doses – 15 mg, 30 mg or 37.5 mg. All three have a phentermine HCL base – which is the concentrated form of phentermine. Each dose has the same amount of Phentermine HCL, so you get the same base in a 37.5 mg that you get in a 30 mg. 

However, the 30 mg gets absorbed into the bloodstream at a much slower pace than the 37.5 mg. So if a patient takes it in the morning, he or she can still keep reaping the benefits 12 hours away. This means he or she will not experience the immediate side effects of the drug – like increased heart rate – all at once – but a steadily elevated heart rate over the course of the day. 

Because of this, 30 mg is usually administered to obese people and older patients, who have higher heart disease risks. This way they’ll be able to experience the effects slowly as the day goes by. 

The more popular phentermine 37.5 mg will be administered to healthier people who can withstand the immediate effects of the drug without needing to slow down said effects. 

But what’s very important to note in phentermine 37.5 mg vs 30 mg is that the 37.5 mg can be further split (since it comes in a tablet form) into two to give an 18.75 mg dose. When you need to gradually stop taking phentermine, your doctor may ask you to split the 37.5 into two and take just each half per day. Before you know it, you’d have ended your dose without suffering withdrawal symptoms. 


You’ll need to think about phentermine 37.5 mg vs 30 mg tables in terms of how fast they affect the body, and how fast you notice their side effects, not in terms of the concentration of the core phentermine HCL base – because they’re all equal in that regard. It’s their effect in the body that differentiates them.

Richard D. Gosnell
Gamer. Wannabe travel fanatic. Avid pop culture expert. Entrepreneur. Extreme social media geek. Professional food trailblazer.