Low-Dose Naltrexone: Appetite & Cravings Changes Explained

Does low-dose naltrexone change appetite or cravings?

The trials that made LDN well known were pain trials. A 2013 crossover trial of 31 women with fibromyalgia measured daily pain, fatigue and sleep on 4.5 mg naltrexone versus placebo [3], and later fibromyalgia trials and a four-trial meta-analysis likewise reported pain and fibromyalgia impact scores [4][9][10][11]. The long COVID work looked at different outcomes: a 2026 systematic review found no randomized trial, and the four before-and-after studies it pooled (155 people, 1 to 6 mg a day) reported fatigue, brain fog, sleep, pain and daily functioning [5].

What the approved naltrexone labels say about appetite

Higher-dose naltrexone does have appetite data, and it runs in both directions.

Vivitrol, the 380 mg monthly injection, lists anorexia, decreased appetite and other appetite disorders among the adverse events that occurred in at least 5% of people with alcohol dependence and at least twice as often as placebo [1]. In that trial the decreased appetite grouping was reported by 14% of the 205 people on 380 mg versus 3% of the 214 on placebo, alongside nausea in 33% versus 11% and vomiting in 14% versus 6% [1].

The 50 mg oral tablet label lists loss of appetite at an incidence under 10% in its clinical trials in opioid addiction, and in the under-1% group it lists increased appetite, weight loss and weight gain [6]. Anorexia also appears among the postmarketing reports [6].

Those are 50 mg and 380 mg products. LDN is usually 4.5 mg, and the labels were written for the approved doses; they give no guidance on LDN doses [6][2].

The animal evidence on palatable food

The most direct experiment on craving-type eating is old and was done in rats. Apfelbaum and Mandenoff fed rats a highly palatable diet for 17 weeks, which produced hyperphagia and overweight; a single injection of naltrexone at 0.5 or 2.5 mg/kg at the start of the dark period suppressed that palatable-diet hyperphagia, while energy intake in control rats eating ordinary chow was unchanged [12]. The authors discussed beta-endorphin involvement in that type of overeating [12]. It is one injected-dose rat experiment, not evidence about a 4.5 mg capsule in people [12].

Are the proposed LDN mechanisms proven?

No. LDN's suggested mechanisms are a brief opioid-receptor blockade with compensatory upregulation of endogenous opioid signalling, and antagonism of TLR4 on microglia; a 2026 narrative review describes these as largely theoretical and speculative [2]. What is established is simpler: naltrexone is a pure opioid antagonist that blocks opioid effects by competitive binding at opioid receptors [6].

Naltrexone plus bupropion is a different product

Contrave is a separate FDA-approved weight-management product that combines naltrexone with bupropion; it is not LDN [7]. In the 56-week COR-I trial, 583 adults were assigned naltrexone 32 mg plus bupropion 360 mg daily, 578 were assigned a lower-dose combination, and 581 were assigned placebo. Mean weight change was -6.1% with the 32 mg combination versus -1.3% with placebo [8]. The Contrave label says coadministration with other naltrexone-containing products is not recommended [7], and it carries a boxed warning for suicidal thoughts and behaviors, which comes from the bupropion component [7]. Its naltrexone dose is several times higher than a usual LDN dose [8][2].

What to watch for

• Nausea, vomiting, headache and dizziness are the label's common effects at approved doses [6][1]. LDN trials describe mostly mild, transient effects, most often insomnia, vivid dreams, nausea and dizziness [2], and a meta-analysis found more vivid dreams and nausea with LDN than with placebo [4].
• Naltrexone is contraindicated in people receiving opioid analgesics and in people currently dependent on opioids, and the label writes that contraindication without a dose exception [6][1]. Precipitated withdrawal from an opioid antagonist can be severe enough to require hospital admission [6].
• No LDN product is FDA-approved. LDN is made mainly by compounding pharmacies, and FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed [2][13]. A 2026 review notes that inconsistencies between compounded formulations add uncertainty [2].