Does Modafinil Cause Weight Gain?

Modafinil is not generally associated with weight gain in the small human studies that have examined appetite and body weight. The available evidence points more toward reduced food intake and, in some settings, less weight gain.

The research is still limited. The studies are small, relatively short, and were designed to answer different questions about appetite, antipsychotic-associated weight gain, and metabolic effects.

Does Modafinil Reduce Appetite or Food Intake?

The clearest evidence that modafinil can affect eating comes from a 2004 study by Makris and colleagues.

Eleven healthy adults completed a series of laboratory sessions in which they received placebo, different doses of modafinil, or different doses of amphetamine. Food was freely available during the sessions, allowing the researchers to measure how much participants actually ate rather than relying only on self-reported appetite.

At the moderate modafinil dose of 3.5 mg/kg, calorie intake fell by about 31% compared with placebo, equivalent to roughly 311 fewer calories over six hours. The reduction came mainly from solid food. Carbohydrate intake also fell significantly, although modafinil did not meaningfully change the overall proportion of calories coming from carbohydrate, fat, and protein.

The study did not show that modafinil caused weight loss. Participants remained within about 2 kg of their baseline weight, and there was no systematic change in body weight across the study. The researchers were measuring the acute effect of individual doses on eating behaviour, not long-term changes in body weight.

Eating less for several hours after a dose does not necessarily translate into sustained weight loss over weeks or months.

Can Modafinil Reduce Weight Gain From Olanzapine?

Olanzapine is an antipsychotic medication used to treat conditions including schizophrenia. It is also well known for causing weight gain in some patients.

Roerig and colleagues tested whether modafinil could reduce that effect. Their 2009 study enrolled 50 healthy volunteers in a three-week randomized, double-blind, placebo-controlled trial. Everyone received olanzapine, while participants were also assigned either modafinil or placebo. Forty completed the study.

Both groups gained weight: those receiving olanzapine plus placebo gained an average of about 2.67 kg over three weeks, while those receiving olanzapine plus modafinil gained about 1.33 kg. BMI also increased less in the modafinil group.

The treatment groups were substantially imbalanced by sex, with no men among the completers in the modafinil group. After the researchers adjusted for gender, the difference in BMI remained statistically significant at week 1 but not at weeks 2 or 3.

Participants taking modafinil generally consumed fewer calories and carbohydrates, but the differences were not statistically significant. Increased appetite was reported by 50% of participants taking olanzapine plus placebo and 22.7% of those taking olanzapine plus modafinil, although that difference also fell short of statistical significance.

The study produced a signal that modafinil might reduce olanzapine-associated weight gain, but the authors specifically cautioned against applying the findings directly to clinical practice.

Does Modafinil Affect Weight in People Taking Clozapine?

Clozapine is another antipsychotic used primarily in schizophrenia, particularly when other treatments have not worked adequately. It can also contribute to weight gain and metabolic problems.

Henderson and colleagues studied whether adding modafinil could improve weight and metabolic measures in people already taking clozapine.

The eight-week randomized, double-blind, placebo-controlled pilot study included 35 participants with schizophrenia or schizoaffective disorder. Nineteen received modafinil and 16 received placebo. Modafinil started at 100 mg/day and could be increased to 300 mg/day.

Participants taking modafinil lost an average of about 0.84 kg, while the placebo group gained approximately 0.01 kg. The difference approached statistical significance for weight but did not reach it. BMI followed a similar pattern.

The researchers also examined glucose, insulin, cholesterol, triglycerides and other metabolic measures. Modafinil did not significantly improve these outcomes compared with placebo. Total calorie intake was lower in the modafinil group, but that difference was also not statistically significant.

The study was small and was not primarily designed or powered to detect modest changes in weight or metabolism. Its results leave open the possibility of an effect without establishing one.

Why Might Modafinil Affect Appetite?

Modafinil affects several brain signalling systems involved in wakefulness and feeding. The Roerig study discusses possible roles for dopamine, norepinephrine, serotonin, histamine, glutamate, GABA and orexin. These systems can influence hunger, arousal and eating behaviour.

The Makris study provides direct behavioural evidence. Participants consumed fewer calories after modafinil, particularly at the moderate dose, without major changes in how often they ate or in the relative proportions of macronutrients they consumed.

The study does not establish which neurochemical effect was responsible for the reduction in food intake.

So Why Might Someone Gain Weight While Taking Modafinil?

The available studies do not show modafinil itself promoting weight gain. If body weight increases during treatment, other factors may be contributing.

Changes in calorie intake, physical activity, sleep, other medications, or the underlying medical condition can all affect body weight. A change occurring while someone is taking modafinil does not by itself establish that modafinil caused it.

Limitations of the Research

The evidence on modafinil and body weight is limited by the size and design of the available studies.

The Makris study included only 11 people and examined acute doses over a matter of hours. The Roerig study lasted three weeks and had a substantial gender imbalance between treatment groups. The Henderson trial included only 35 participants and lasted eight weeks.

Two of the three studies also involved olanzapine or clozapine, antipsychotic medications that can themselves strongly affect body weight and metabolism. Those findings therefore cannot be assumed to represent what happens in someone taking modafinil without an antipsychotic.

There is little direct evidence showing what happens to body weight over months or years in people taking modafinil for its usual clinical indications.

Bottom Line

Modafinil is not established as a weight-loss drug, but current human research also does not support weight gain as a typical effect.

A small laboratory study found that modafinil could reduce short-term calorie intake. Studies involving olanzapine and clozapine found either less weight gain or a modest, statistically uncertain reduction in weight. None demonstrates reliable long-term weight loss.

References

Henderson, D. C., Freudenreich, O., Borba, C. P. C., Wang, X., Copeland, P. M., Macklin, E., Fan, X., Cather, C., & Goff, D. C. (2011). Effects of modafinil on weight, glucose and lipid metabolism in clozapine-treated patients with schizophrenia. Schizophrenia Research, 130(1–3), 53–56. https://doi.org/10.1016/j.schres.2011.04.009

Makris, A. P., Rush, C. R., Frederich, R. C., & Kelly, T. H. (2004). Wake-promoting agents with different mechanisms of action: Comparison of effects of modafinil and amphetamine on food intake and cardiovascular activity. Appetite, 42(2), 185–195. https://doi.org/10.1016/j.appet.2003.11.003

Roerig, J. L., Steffen, K. J., Mitchell, J. E., Crosby, R. D., & Gosnell, B. A. (2009). An exploration of the effect of modafinil on olanzapine associated weight gain in normal human subjects. Biological Psychiatry, 65(7), 607–613. https://doi.org/10.1016/j.biopsych.2008.10.037