Sexual Side Effects of Phentermine

Phentermine is a weight loss drug that has been prescribed for decades. It became popular in the 1990s as "Phen-Phen" (when combined with Pondemin, no longer on the market). Phentermine revs the metabolism in a way that allows someone to want to eat less. It's also a symphatomimetic drug that makes the body feel in "fight or flight" mode. It's not that you feel full with Phentermine; it's more like you are too energized to be hungry. Like many weight loss stimulants, it has a few side effects--sexual side effects being just one. You can stop using Phentermine if you experience sexual side effects, but most doctors say that they will diminish with continued use of the drug.

Loss of Desire

Some men and women report that they have a loss of sexual desire while taking Phentermine. This is thought to be the tendency that diet pills have on the nervous system. Because the body is revving for fight or flight through a chemical means, your body is busy doing work even when you are at rest or relaxing. And relaxation is very important for sexual desire. Someone taking Phentermine might find he has less interest in sex because of this. Still, weight loss can serve as an inducement and excitement about sex that someone had perhaps never experienced before. Let the drug work on your weight and then recheck your libido. Talk to your doctor if the problem persists.

Loss of Erection

Men using Phentermine might experience erectile dysfunction as a side effect. This is true for men who are experiencing this dysfunction with a partner, as well as not having the very common morning erection. The erectile dysfunction isn't connected to desire in any way; it's physiological. Plenty of drugs exist to help with ED, but talk to your prescribing doctor if you have trouble with erections. Many men who continue to take Phentermine experience a return to what is normal for them in a few weeks.

Loss of Size and Dimension

Don't panic. Some men report that the size of their testicles and penis diminishes slightly. Again, the fight or flight instinct that is created artificially from Phentermine is at the root of the cause. This kind of minor size reduction can sometimes make men discontinue use of the drug. However, it's considered temporary and all things will return to a normal size when your body gets more used to the drug.


Nothing is better for sexual mood and performance than relaxation. But weight loss drugs including Phentermine have the tendency to make a person a little edgy, anxious and moody. This is another way that Phentermine can affect sexual desire and sexual health. Your body can adjust to the drug and the moodiness, and anxiety can diminish. But if you find yourself in a constant sour mood and have no interest in things like sex, consult your doctor.

Phentermine and Healthy Sex

Again, weight loss is a huge ego boost and usually gives someone energy and excitement because of the change in her outward appearance. This helps increase a sense of self and, perhaps, increase sex drive. So if you have sexual side effects from Phentermine in the beginning, try to see if they disappear in a few weeks. Eat healthy and drink lots of water to help flush your system. And exercise. A complete and healthy weight loss program will involve physical exercise, which will help to remove toxins from prescription medications as you sweat. If the side effects don't diminish or go away, ask your doctor for another type of weight loss drug.