Phentermine-Effexor: Is it effective? An interview with Dr. Paul Rivas

By Larry Hobbs
Saturday, January 08, 2005

Paul Rivas, M.D. is an internist in the Baltimore area who is using the combination of phentermine and Effexor (venlafaxine) with good success. Larry Hobbs interviewed Dr. Rivas by phone.

Hobbs: How many patients have you treated with Phen-Effexor?

Rivas: About 500.

Hobbs: What dose do you use?

Rivas: A 37.5 mg caplet of phentermine given either once in the morning, or split between morning and afternoon. This combined with 37.5 mg of the extended-release Effexor—Effexor-XR. It can be taken either in the morning, or at night if a patient says that it makes them sleepy. Because it’s extended-release the timing of the Effexor doesn’t seem to matter that much.

Hobbs: Do you prefer the extend-release?

Rivas: Yes. The extended-release doesn’t cause the nausea like I saw with the immediate-release.

Hobbs: How much weight loss have you seen?

Rivas: Up to 75 or 80 pounds in some patients. In about a third of patients it works just great. Universally those patients say “It was like turning off a switch.” For the other two-thirds, it’s not as dramatic. They lose 20 or 25 pounds on average, but it’s still a struggle. The medicines help, but they don’t completely eliminate cravings.

Hobbs: Do you think craving control is important?

Rivas: Yes–very important. I think the major reason that most of my patients are overweight is because of sweet cravings, compulsive eating and appetite. Most of them have at least one, and some have all three. I believe that if you control these three things, patients will lose weight without any major changes in the rest of their diet.

Hobbs: Is Effexor a serotonin reuptake inhibitor?

Rivas: Actually it blocks both serotonin and noradrenaline reuptake, however it’s 5 times more potent at blocking serotonin reuptake.

Hobbs: What other combinations have you tried?

Rivas: Phen-Prozac, Phen-Zoloft, Phen-Serzone, Phen-Phendimetrazine and Phen-Wellbutrin.

Hobbs: How does Phen-Effexor compare to Phen-Prozac or Phen-Zoloft?

Rivas: I think they are equally effective, but I prefer the Effexor because it doesn’t cause sexual dysfunction, particularly delayed orgasm, that some patients complain about with Prozac. Secondly, patients don’t have a bias against Effexor like some do against Prozac.

Hobbs: What did you find with Phen-Serzone?

Rivas: The biggest problem was sleepiness. Patients complained of feeling tired and not being able to wake up. I couldn’t get around this. Even increasing the dose of phentermine didn’t seem to help.

Hobbs: How effective was Phen-Phendimetrazine?

Rivas: Ok, but not great. It’s somewhat better than phentermine alone, but not as effective as Phen-Effexor. But I found I could get the same effect by doubling the dose of phentermine, so I’ve stopped using phendimetrazine.

Hobbs: How about Phen-Wellbutrin?

Rivas: I’ve had very good success with it. I know that other physicians say that it doesn’t work, but it works for me. The only problem is that patients build up a tolerance after about two months. At that time I’ll switch them to something else and then switch back later.

Hobbs: What patients do best with Phen-Wellbutrin?

Rivas: Patients who haven’t responded to one of the serotonin reuptake inhibitors like Effexor or Prozac often do well with Phen-Wellbutrin. I’ve used it with about 50 patients.

Hobbs: How much Wellbutrin do you use?

Rivas: 150 mg of the sustained-release Wellbutrin-SR once or twice a day. But I make sure doses are spaced at least eight hours apart because there is a small increased risk of seizure that you need to be cautious about.

Hobbs: What are the side effects with Phen-Effexor?

Rivas: It increases migraines in patients who are prone to that. Other than that it’s just nuisance side effects like dry mouth, sleepiness or insomnia, but the last two can be controlled by changing the timing of the dose.

Hobbs: What is your experience with Phentermine alone?

Rivas: Phentermine is an excellent appetite suppressant, but it doesn’t control sweet cravings and compulsive eating which fenfluramine did. But I’ve found that adding the Effexor helps to take care of the sweet cravings and compulsive eating.

Paul Rivas, M.D. can be reached at:

Rivas Medical Weight Loss Program
1205 York Rd
Lutherville, MD 21093
(410) 583-5677 phone
(410) 583-5680 fax