Many antidepressants are associated with changes in weight. Unlike other medications that trigger weight gain as a potential side effect, Prozac may actually create a short-term reduction of weight. It is unclear whether the weight change is a direct result of the medication or an indirect impact from changing levels of depression and anxiety.
Increased Risk of Suicidal Thoughts and Behaviors Prozac has a boxed warning for increased risks of suicidal thoughts and behaviors. This is a warning from the Food and Drug Administration (FDA); therefore, a qualified doctor should prescribe the medication.
What Are Antidepressants?
Antidepressants are a broad class of medications that work primarily totreat the signs and symptoms of various types of depression. These medications for depression modify the chemical messengers in the brain to target the effects of depression and promote well-being.1 Contrary to what the name suggests, professionals prescribe antidepressants for concerns other than depression.
Antidepressants can also help treat:1,2
- Other mood disorders like bipolar disorder
- Anxiety disorders like panic disorder
- Eating disorders
- Post-traumatic stress disorder (PTSD)
- Pain
- Insomnia
There are many types of antidepressants. Each group works differently by interacting with a specific neurotransmitter or group of neurotransmitters. Prozac (fluoxetine) is a selective serotonin reuptake inhibitor (SSRI). It treats mental health conditions by blocking the reabsorption of serotonin, so more is available in the brain.
Other antidepressants, like Effexor (venlafaxine), are serotonin and norepinephrine reuptake inhibitors (SNRIs). These medications affect the reabsorption of norepinephrine and serotonin.1
Can Antidepressants Cause Weight Loss?
As a class of medications, antidepressants are known to trigger changes in weight. Most frequently, these medications are associated with weight gain, but on occasion, weight loss may also occur. Prozac is linked to weight loss, especially early in treatment.3,4 Studies show that when people begin treatment with Prozac, they could experience a modest weight loss of about one pound.
This weight loss will be observable about one month after beginning treatment. The weight loss will not be permanent, but it seems to continue throughout the first three months of treatment with Prozac. Like other medication results, not everyone will lose weight on Prozac. Of those studied, though, the weight loss was fairly consistent.
When researchers tracked patients for six months and more, the people gained back the original weight. In some cases, they added an average of six pounds in the year after starting treatment.3,4 Although this may seem significant, the weight gained on Prozac is comparable or lower than similar antidepressants. Antidepressants are more often related to weight gain rather than weight loss.
Antidepressants that cause weight loss may include:
- Prozac (fluoxetine)
- Wellbutrin (buprinopine)
Like Prozac, Wellbutrin seems associated with short-term weight loss. At the 3-month mark, patients report some weight loss on average. Then, weight seems to increase slightly at 6-month and 9-month reviews. By the one year mark, average weight is similar to the original baseline levels.3
Antidepressants & Weight Gain
The more common effect of antidepressants is to trigger weight gain in patients. Some gains may be immediate, delayed, continuous, or temporary with plateaus. Older medications are more strongly linked to weight gain and other unwanted effects, but even the newest generations of antidepressants may produce weight gain.
Antidepressants that cause weight gain may include:3,5
- Amitriptyline, Tofranil (imipramine) and doxepin: types of tricyclic antidepressants
- Nardil (phenelzine) and other monoamine oxidase inhibitors (MAOIs)
- Paxil (paroxetine) and Celexa (citalopram): two types of selective serotonin reuptake inhibitor
- Effexor (venlafaxine): a commonly used serotonin and norepinephrine reuptake inhibitor
- Remeron (mirtazapine): an atypical antidepressant
Some medications cause weight gain that seems to level out over the course of a few months. Other medications, like Effexor (venlafaxine) and Remeron (mirtazapine), seem to trigger weight gains that continue to increase with time.1
The primary goal of antidepressants is to manage the patient’s mental health symptoms, but a rapid weight gain could prove problematic, especially if the person is already overweight at the beginning of treatment. The decision to continue or end treatment must be a conversation between the prescriber and the patient as they consider the risks and benefits of continued treatment.
Why Does Prozac Cause Weight Loss?
No one can state with precision why some antidepressants trigger weight gain and why others, like Prozac, seem to produce weight loss. Much of the impact has to do with individual differences, depressive symptoms, and expected weight gain in adults.
The weight changes during depression and anxiety are complex situations. Some people will note decreased appetite with weight loss that follows when symptoms are high. Others will find that high symptoms are linked to increased appetite and weight gain.4
The weight loss that comes with Prozac could be a sign that depression is alleviating. As symptoms reduce, the overeating and weight gain that comes with it begins to fade. This change allows people to lose some depression-related weight.5
The decreased depressive symptoms could also spark an increase in energy and motivation. With more physical activity, the person could shed some weight in the early months of Prozac treatment.
When Prozac Weight Loss Becomes a Problem
Significant weight loss is a concern when people use Prozac. The concern is more troubling when it occurs in very underweight people who are depressed or living with bulimia nervosa, an eating disorder.6 A person with an eating disorder could continue to lose weight because the Prozac treatment is not doing enough to manage symptoms.
Among people treated with Prozac for bulimia nervosa, 8% experienced decreased appetite. Among those with depression, 11% experienced decreased appetite. Among those with obsessive-compulsive disorder (OCD), 17% experienced decreased appetite.6
If you find that you or a loved one are losing significant weight, make a call to the prescriber or primary care physician. They can assess the severity of the weight loss and recommend appropriate care to lower the risk.
How to Prevent Prozac Weight Loss
At the beginning of your treatment with Prozac, have a conversation with your doctor about the risks and benefits. Discuss the potential for weight loss, what you should do about it, and when to be concerned with the impact. Preventing Prozac weight loss may not be the most important goal. Instead, it could be a better decision to focus on improving your mental health concerns.
Consider weighing yourself weekly to assess and track any changes in your weight. Then, work with your prescriber to note when weight loss could become problematic.
If weight loss continues, work with your doctor to:
- Change the dose: the amount of Prozac you take could result in more weight loss. The prescriber may increase or decrease as needed to minimize unwanted changes.
- Switch medications: if the side effects are too great, another medication may be the best course of action.
- Shift your diet and exercise routines: take some time to reflect on your habits to see if you can adjust your intake or physical activity to slow the weight loss.
- Work with professionals: dietitians and personal trainers can use their expertise to manage your weight. Trusting their education and experience can help reduce the effects of Prozac.
When to Speak With Your Doctor
Any time you are using Prozac to manage symptoms of depression, anxiety, or another condition, you should have consistent communication with your doctor. From the first dose to the most recent refill, having an open and honest dialogue to minimize the risk of side effects. It can also help you catch problems early.
At any point of your treatment, you could benefit from asking your doctor questions that address your concerns and improve your safety. Your doctor should patiently answer your questions and relieve your worries.
Consider asking your doctor these questions:1
- Why do you think Prozac is best for me?
- What are the possible side effects of antidepressants?
- Do I need to change my diet or exercise while taking this medication?
- How do people usually respond to this medication?
- What should I do if I begin experiencing side effects for this medication?
- What type of weight changes should I expect from this medication?
Final Thoughts
While Prozac’s side effects may include weight loss for some, every individual responds differently. It’s important to speak with your doctor about any side effects you may have and how to best manage them. Most often, the weight loss will be moderate before you return to your starting weight several months after treatment begins. It should dissuade you from trying Prozac to manage your mental health.
Prozac & Weight Loss Infographics
