Naltrexone is not a stimulant. It is classified as a pure opioid antagonist, meaning it blocks opioid receptors in the brain rather than increasing alertness, energy, or nervous system activity the way stimulants do. The FDA approved it to treat opioid use disorder and alcohol use disorder, and it works by sitting on opioid receptors without activating them, which prevents opioids and alcohol from producing their usual rewarding effects.
How Naltrexone Actually Works
Stimulants like amphetamine or methylphenidate increase levels of dopamine and norepinephrine to boost focus, wakefulness, and heart rate. Naltrexone does none of that. Instead, it latches onto the same receptors that opioids target and locks them down. It binds tightly to the mu opioid receptor (the primary receptor responsible for the “high” from opioid drugs) and also attaches to kappa and delta opioid receptors. Because it occupies these sites without switching them on, it effectively blocks opioids from having any effect. The FDA label describes it as having “no opioid agonist properties,” meaning it produces no opioid-like high, sedation, or pain relief on its own.
For people with alcohol use disorder, blocking opioid receptors reduces the pleasurable buzz that alcohol normally triggers through the brain’s endorphin system. Over time, drinking becomes less rewarding, which helps people cut back. The standard dose for alcohol use disorder is 50 mg once daily. For opioid use disorder, treatment typically starts at 25 mg to confirm no withdrawal symptoms occur before moving to the full 50 mg daily dose.
Why Some People Think It Feels Stimulating
The confusion likely comes from side effects that overlap with what stimulants produce. Some people taking naltrexone report insomnia, restlessness, anxiety, or jitteriness. These aren’t signs that naltrexone is revving up the nervous system the way caffeine or Adderall would. They’re more likely the result of blocking the body’s own endorphins, which normally help regulate mood, sleep, and stress responses. When those calming signals are dampened, some people feel an uncomfortable edginess that mimics stimulant-like sensations.
Another source of confusion is the combination drug that pairs naltrexone with bupropion for weight management. Bupropion is a norepinephrine and dopamine reuptake inhibitor, which does have mild stimulant-like properties. That combination targets both the brain’s appetite-regulating system and its reward circuitry to reduce food cravings. But the stimulant-adjacent effects come from the bupropion half of the pill, not from naltrexone itself.
Naltrexone and Stimulant Medications Together
Naltrexone doesn’t interact with stimulants the way two similar drugs might amplify each other. In fact, research from Massachusetts General Hospital found that naltrexone does the opposite: it reduces the euphoria that stimulants can produce. In a clinical trial, young adults with ADHD received methylphenidate (Ritalin) along with either 50 mg of naltrexone or a placebo daily for six weeks. At the three-week mark, those taking naltrexone showed significantly less euphoria from a high dose of the stimulant compared to the placebo group. This suggests naltrexone could potentially help reduce the abuse potential of stimulant medications rather than adding to their effects.
Low-Dose Naltrexone and Energy Levels
A separate point of confusion involves low-dose naltrexone (LDN), which uses much smaller amounts (typically 3 to 4.5 mg) compared to the standard 50 mg dose. At these low doses, naltrexone appears to work as an immune modulator rather than a straightforward opioid blocker. The leading theory is that briefly blocking opioid receptors triggers a rebound surge in the body’s natural endorphin production, or that the drug directly reduces inflammation driven by immune cells in the brain.
Some people using LDN for conditions like chronic fatigue syndrome, fibromyalgia, or autoimmune disorders report increased energy, improved mood, and reduced pain. A case report published in BMJ Case Reports documented a patient with chronic fatigue syndrome who experienced gradual improvements in energy, mood, and pain tolerance as her LDN dose was increased to 4.5 mg daily. These energy improvements can feel stimulating to someone who has been fatigued for years, but the mechanism is fundamentally different from how a stimulant works. LDN appears to reduce the underlying inflammation and immune dysfunction dragging energy levels down, rather than artificially boosting alertness.
How Naltrexone Compares to Stimulants
- Drug class: Naltrexone is an opioid antagonist. Stimulants are sympathomimetic agents that activate the sympathetic nervous system.
- Abuse potential: Naltrexone has no abuse potential and is not a controlled substance. Most prescription stimulants are Schedule II controlled substances.
- Effect on dopamine: Stimulants directly increase dopamine availability. Naltrexone indirectly modulates dopamine by blocking opioid receptors in reward pathways, which tends to reduce pleasure signals rather than amplify them.
- Physical effects: Stimulants raise heart rate, blood pressure, and alertness. Naltrexone does not produce these cardiovascular or arousal effects.
- Withdrawal risk: Stopping stimulants after prolonged use can cause fatigue and depression. Stopping naltrexone does not produce physical withdrawal symptoms.
Naltrexone sits in a completely different pharmacological category from stimulants. Any energizing or activating sensations people experience while taking it are side effects of opioid receptor blockade, not evidence that the drug is stimulating the central nervous system.