Several widely prescribed drug classes can dramatically increase appetite and food intake, sometimes leading to significant weight gain within weeks of starting treatment. Antipsychotics, corticosteroids, certain antidepressants, antiepileptic medications, and even common antihistamines all rank among the most common culprits. The mechanisms vary from one drug to the next, but many converge on a shared theme: they interfere with the brain’s hunger and reward signaling in ways that make you eat more, crave richer foods, or feel less satisfied after a meal.
Antipsychotic Medications
If there is a single drug class most notorious for driving appetite through the roof, it is atypical (second-generation) antipsychotics. Medications like olanzapine, clozapine, quetiapine, and risperidone are prescribed for conditions ranging from schizophrenia and bipolar disorder to off-label uses for insomnia and anxiety. The appetite increase with some of these drugs is not subtle. Patients frequently describe an almost insatiable hunger, particularly for carbohydrate-rich and fatty foods, that sets in within the first few weeks of treatment.
The strongest explanation centers on histamine. These drugs block histamine H1 receptors in the hypothalamus, which is the brain region that acts as a thermostat for hunger and energy balance. When H1 receptors are blocked, a signaling cascade ramps up calorie intake and, over time, promotes fat accumulation while also reducing energy expenditure.1SpringerLink / CNS Drugs. The role of hypothalamic H1 receptor antagonism in antipsychotic-induced weight gain Olanzapine and clozapine have the strongest H1 antagonism among antipsychotics, which helps explain why they consistently cause the most weight gain. Aripiprazole, by contrast, has weaker H1 effects and tends to be more weight-neutral.
The weight gain with these drugs is not just about eating more. Multiple hormonal pathways shift simultaneously: leptin (the hormone that signals fullness) rises but seems to lose its effectiveness, insulin levels climb, and triglycerides increase. A genome-wide association study found that variants near the melanocortin 4 receptor gene, a region already linked to obesity risk in the general population, were strongly associated with extreme antipsychotic-induced weight gain. People who carried two copies of the risk variant gained dramatically more weight over a 12-week trial than those who did not.2JAMA Psychiatry. Association Between Common Variants Near the Melanocortin 4 Receptor Gene and Severe Antipsychotic Drug–Induced Weight Gain In other words, the same drug can hit two people very differently depending on their genetic makeup.
Corticosteroids
Prednisone, dexamethasone, and other corticosteroids are among the most commonly prescribed anti-inflammatory drugs, used for everything from asthma flares and autoimmune conditions to organ transplant management. Ask anyone who has been on a course of prednisone lasting more than a few days, and they will likely mention the hunger. Some people describe it as a gnawing, relentless appetite that makes them raid the kitchen at hours they normally would not eat.
Glucocorticoids disrupt the hormones that normally regulate appetite. Overexposure to these drugs can impair signals from hormones that control reward-related eating, which may lead to a loss of normal appetite regulation and compulsive eating behavior.3Europe PMC. Glucocorticoids, stress and eating: The mediating role of appetite-regulating hormones The body’s own cortisol, the natural glucocorticoid released during stress, does something similar. When you take synthetic corticosteroids, the effect is amplified because the doses often far exceed what your body would produce on its own. Weight gain from corticosteroids tends to concentrate around the abdomen and face, a pattern distinct from the more generalized weight gain seen with antipsychotics.
Antidepressants That Increase Appetite
Not all antidepressants cause weight gain equally, and a few are particularly well known for ramping up hunger. Mirtazapine stands out. It is an effective antidepressant with strong sedating properties, often prescribed specifically for people who have trouble sleeping or who are underweight. The appetite-boosting effect is actually considered a benefit in some clinical situations, like treating elderly patients with depression-related weight loss.
Mirtazapine is a potent antagonist at histamine H1 receptors, which is the same mechanism behind antipsychotic-driven hunger.4SpringerOpen (Naunyn-Schmiedeberg’s Archives of Pharmacology). Weight-gain independent effect of mirtazapine on fasting plasma lipids in healthy men The H1 blockade appears to be the key driver of the increased appetite, rather than the serotonin or norepinephrine effects that give the drug its antidepressant action. Other antidepressants associated with weight gain include paroxetine (a selective serotonin reuptake inhibitor) and amitriptyline (an older tricyclic), both of which also have antihistamine properties, though their appetite effects are generally less dramatic than mirtazapine’s.
Selective serotonin reuptake inhibitors as a class have a more complicated picture. Some people lose weight early in treatment because these drugs can suppress appetite initially, only to see the effect reverse after several months. The long-term weight gain with SSRIs is more modest on average and may not be primarily driven by appetite increases so much as by metabolic shifts and improved mood leading to normalized eating patterns in people who were previously undereating due to depression.
Antiepileptic and Neuropathic Pain Medications
Seizure medications are a mixed bag when it comes to appetite. Valproate (valproic acid) and carbamazepine are among those most consistently linked to increased eating and weight gain. The mechanism may involve enhancing a brain signaling system that uses a neurotransmitter called GABA, which can increase appetite for carbohydrate-heavy foods and reduce energy expenditure at the same time.5PubMed. Bodyweight gain and anticonvulsants: a comparative review Gabapentin and pregabalin, which are widely used for nerve pain and anxiety in addition to seizures, also frequently increase appetite and cause weight gain, though the exact pathway is less well characterized.
On the flip side, several antiepileptics go in the opposite direction. Topiramate and zonisamide tend to suppress appetite and are sometimes even prescribed off-label for weight loss. This split within a single drug class is a good example of why blanket statements about medications and appetite are rarely useful. Two drugs prescribed for the same condition can push hunger in opposite directions.
Antihistamines
Most people think of antihistamines as allergy pills, not appetite stimulants. But older, first-generation antihistamines like cyproheptadine are potent appetite boosters. In fact, cyproheptadine is specifically used in clinical practice to stimulate appetite in underweight patients and children who are poor eaters. A randomized, placebo-controlled trial found that patients taking cyproheptadine experienced significantly greater appetite improvement and gained more weight and body mass compared with those on placebo.6PubMed Central. Efficacy and Tolerability of Cyproheptadine in Poor Appetite: A Multicenter, Randomized, Double-blind, Placebo-controlled Study
Newer, second-generation antihistamines like cetirizine and loratadine are designed to have less effect on the brain and therefore cause less drowsiness. They are also less likely to cause significant appetite increases, though some people do report increased hunger with long-term use. The connection between histamine and appetite is the same thread running through antipsychotics and mirtazapine: when you block H1 receptors, especially in the brain, you tend to feel hungrier.
Benzodiazepines
Benzodiazepines like diazepam, alprazolam, and lorazepam are prescribed for anxiety, insomnia, and seizures. They work by enhancing GABA activity in the brain, which produces their calming and sedating effects. But this same mechanism appears to have a side effect on eating behavior that is less well known: benzodiazepines enhance how pleasurable food tastes. The primary action is not that they make you feel hungrier in a stomach-growling sense but that they make eating feel more rewarding, so you eat more of whatever is in front of you and are more motivated to seek out food.7Appetite. Palatability-dependent appetite and benzodiazepines: new directions from the pharmacology of GABAA receptor subtypes
This mechanism is subtler than the raw hunger caused by corticosteroids or antipsychotics. You might not notice a change in baseline appetite, but you may find yourself polishing off an entire bag of chips when you normally would have stopped halfway. The increased eating is driven by the pleasure of the food rather than by physiological hunger signals, which makes it harder to recognize as a drug effect.
Cannabis
The “munchies” associated with cannabis use are one of the most culturally familiar examples of drug-induced appetite. THC, the primary psychoactive compound in cannabis, activates receptors in brain regions involved in hunger and in the perception of taste and smell. The result is a double hit: you feel hungrier, and food tastes and smells more appealing than usual. This effect is robust enough that synthetic cannabinoid medications like dronabinol have been approved to stimulate appetite in patients with AIDS-related wasting and chemotherapy-related nausea.
One of the distinctive features of cannabis-induced hunger is its focus on highly palatable, calorie-dense foods. People under the influence of THC tend to gravitate toward sweet, salty, and fatty options rather than, say, steamed broccoli. The effect is temporary, lasting only as long as the drug is active, but regular users may still see weight changes over time depending on their frequency and pattern of use.
Diabetes Medications That Trigger Hunger Through Low Blood Sugar
Some diabetes medications increase appetite not by directly acting on hunger circuits but by occasionally dropping blood sugar too low. Sulfonylureas, a widely prescribed class of oral diabetes drugs, stimulate the pancreas to release insulin. When insulin output overshoots, blood sugar dips, and the body responds with hunger signals designed to make you eat and restore glucose levels. A large observational study of sulfonylurea use in real-world practice found that patients experienced a small but statistically significant increase in body mass index over the course of treatment, and hypoglycemia scores were correlated with the increase.8PubMed Central. Usage pattern, glycemic improvement, hypoglycemia, and body mass index changes with sulfonylureas in real-life clinical practice: results from OBSTACLE Hypoglycemia Study
Insulin itself can cause the same pattern. When injected insulin doses are a bit too high, blood sugar falls, and the resulting hunger can be intense and difficult to resist. Over time, this cycle of low blood sugar followed by compensatory eating can contribute meaningfully to weight gain, which is frustrating for people with type 2 diabetes who are often trying to lose weight as part of their treatment plan. Newer diabetes drug classes like GLP-1 receptor agonists (semaglutide, liraglutide) and SGLT2 inhibitors were developed in part to avoid this appetite-stimulating side effect, and they actually tend to promote weight loss instead.
Sleep Medications and Unconscious Eating
Zolpidem (sold as Ambien) is a widely used sleep aid that occasionally causes an unusual side effect: people get up in the night and eat, sometimes in large quantities, with little or no memory of doing it. This phenomenon, sleep-related eating disorder, has been documented repeatedly in case reports and literature reviews. Patients typically have partial or complete amnesia about their nighttime eating episodes, which can involve bizarre food combinations, uncooked foods, or even non-food items.9Sleep Medicine: X. Sleep-related eating disorder associated with zolpidem: cases compiled from a literature review
The eating behavior appears to emerge during a state of partial arousal from sleep. Patients who already have underlying sleep disorders that cause frequent awakenings may be more vulnerable.10PubMed. Amnestic sleep-related eating disorder associated with zolpidem The good news is that the eating episodes stop when the medication is discontinued.11PubMed Central. Zolpidem and amnestic sleep related eating disorder This is worth knowing because many people who experience this side effect do not connect their mysterious kitchen messes or unexplained weight gain to their sleep medication. If you take zolpidem and find evidence of nighttime eating you do not remember, bring it up with your prescriber.
The Rebound Effect When Appetite-Suppressing Drugs Are Stopped
Some drugs do not make you eat more while you are taking them. Instead, the surge in hunger arrives when you stop. This rebound effect is well documented with stimulant medications and, more recently, with GLP-1 receptor agonists used for weight loss.
Amphetamines and other stimulants suppress appetite while active, which is why some are used off-label for weight loss. But animal research shows that after chronic amphetamine administration is discontinued, subjects ate significantly more standard food and gained more weight than controls who had never received the drug.12PubMed Central. Food consumption and weight gain after cessation of chronic amphetamine administration The body appears to overshoot in the opposite direction once the appetite-suppressing signal is removed.
The same principle applies to GLP-1 receptor agonists like semaglutide and tirzepatide. These drugs suppress appetite powerfully while you take them, but discontinuation triggers a rebound in hunger driven by the reactivation of appetite-stimulating hormonal pathways and a compensatory rise in ghrelin, the so-called “hunger hormone.”13PubMed Central. Early Weight Regain After GLP-1 Receptor Agonist Discontinuation: Mechanisms and Implications for Treatment De-Escalation Strategies The biological drive to regain weight reflects deeper adaptations to weight loss itself, including shifts in metabolic rate and changes in how the brain processes hunger signals.14PubMed. Clinical Management of Weight Regain and Cardiometabolic Consequences After Discontinuation of GLP-1 Receptor Agonists Abrupt discontinuation creates a mismatch: the strong biological push to eat returns all at once while the pharmacological brake vanishes. This helps explain why weight regain after stopping these medications is so common and often rapid.
How the Brain’s Reward System Ties It All Together
Many of these drug effects converge on a common piece of brain wiring: the mesolimbic dopamine system, which governs motivation, reward, and reinforcement. This circuit does not just control pleasure from eating; it shapes how motivated you feel to seek out food in the first place. Multiple hormones involved in appetite regulation interact directly with this dopamine system, and the activity of the circuit changes with fasting, food restriction, and the development of obesity.15Europe PMC. Actions of feeding-related peptides on the mesolimbic dopamine system in regulation of natural and drug rewards
When a drug blocks histamine receptors (antipsychotics, mirtazapine, cyproheptadine), enhances GABA signaling (benzodiazepines, valproate), disrupts appetite hormones (corticosteroids), or activates cannabinoid receptors (THC), the downstream effects often ripple through this same reward circuitry. That is why drug-induced overeating often feels less like hunger and more like craving. The drive to eat is not always coming from the stomach; it is coming from a brain reward system that has been nudged off its usual set point.
Managing Drug-Induced Appetite
If a medication is making you eat significantly more, the first conversation should be with your prescriber about whether an alternative drug with a lower appetite profile exists. Within antipsychotics, switching from olanzapine to aripiprazole or ziprasidone can make a meaningful difference. Among antidepressants, bupropion is generally weight-neutral or even mildly appetite-suppressing, making it a possible alternative to mirtazapine when weight gain is a concern. For seizure drugs, topiramate is less likely to stimulate appetite than valproate.
When switching is not an option because the current drug is the one that works, adding metformin has the strongest evidence base for offsetting antipsychotic-induced weight gain specifically. A meta-analysis found that metformin reduced body weight by about 5 kg compared with placebo over 12 weeks in patients taking olanzapine.16PubMed Central. Metformin for olanzapine-induced weight gain: a systematic review and meta-analysis More recently, consensus guidelines have recommended co-starting metformin with an antipsychotic from the outset to prevent weight gain rather than waiting to treat it after the fact. Starting metformin alongside the antipsychotic can reduce weight gain by roughly 4 kg compared with controls.17Schizophrenia Bulletin. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation
Behavioral strategies like structured meal timing and keeping high-calorie convenience foods out of the house can help, but they are fighting against a pharmacological signal, which is a hard battle to win with willpower alone. Recognizing that the increased hunger is a drug effect and not a personal failure is important both for the person taking the medication and for their care team. Drug-induced appetite increases are biological, not psychological, and they require medical solutions rather than just dietary advice.
Drugs Designed to Make You Eat More
Not all drug-induced appetite increase is a side effect. For people with cancer cachexia, AIDS wasting, or severe anorexia, stimulating appetite is the whole point. Megestrol acetate is a synthetic progestational agent used specifically for this purpose. A Cochrane systematic review found that roughly one in four patients taking megestrol experienced a meaningful improvement in appetite, and the drug was associated with slight weight gain compared with placebo across studies involving cancer, AIDS, and other serious illnesses.18Cochrane Database of Systematic Reviews. Megestrol acetate for treatment of anorexia‐cachexia syndrome Those numbers sound modest, but for patients who have lost the ability to eat normally, even a small increase in appetite can improve quality of life.
A newer frontier involves drugs that mimic ghrelin, the hormone your stomach releases when it is empty. Anamorelin is a synthetic ghrelin receptor agonist developed for cancer-related appetite loss. In animal studies, it significantly increased both food intake and body weight in a dose-dependent manner.19PubMed Central. Anamorelin HCl (ONO-7643), a novel ghrelin receptor agonist, for the treatment of cancer anorexia-cachexia syndrome: preclinical profile Researchers have also explored other synthetic compounds that activate the ghrelin receptor even more potently than the body’s own ghrelin signal.20Scientific Reports. A Novel Non-Peptidic Agonist of the Ghrelin Receptor with Orexigenic Activity In vivo These drugs represent an attempt to harness the very mechanisms that cause unwanted hunger with other medications and put them to therapeutic use.
Can Probiotics Blunt the Effect?
Given the growing interest in the gut microbiome, researchers have tested whether manipulating gut bacteria could offset drug-induced appetite and weight gain. One study gave Bifidobacterium (a common probiotic strain) alongside olanzapine to patients starting the antipsychotic. At four weeks, the probiotic group gained less weight: about 1.1 kg compared with 2.4 kg in the group receiving olanzapine without the probiotic. But the difference disappeared by eight and twelve weeks, and the probiotic had no measurable effect on appetite at any time point.21SpringerLink / Psychopharmacology. Effect of Bifidobacterium on olanzapine-induced body weight and appetite changes in patients with psychosis
The result is characteristic of where the microbiome field stands for many drug side effects: intriguing early signals that fade with longer follow-up. A brief delay in weight gain is not nothing, but it is far from a reliable countermeasure. Metformin, as described earlier, currently has much stronger evidence. The probiotic angle is worth watching, but it is not yet something to rely on if you are struggling with drug-induced overeating.