Kratom is not a classical opioid, but its primary active compounds bind to the same brain receptors that opioids do. This puts it in an unusual gray area: it produces opioid-like effects, can cause physical dependence, and triggers withdrawal symptoms that closely resemble opioid withdrawal, yet it differs from drugs like morphine and oxycodone in important ways. The answer depends on whether you define “opioid” by its chemistry, its receptor activity, or its legal classification.
How Kratom Acts on Opioid Receptors
Kratom leaves contain more than 40 alkaloids, but two do most of the heavy lifting. Mitragynine makes up 40% to 60% of the total alkaloid content and is the primary active compound. The second, 7-hydroxymitragynine, is present in much smaller amounts but binds to the brain’s mu-opioid receptors roughly nine times more strongly than mitragynine does.
Mu-opioid receptors are the same targets activated by morphine, codeine, heroin, and prescription painkillers. When a substance binds to these receptors, it can produce pain relief, sedation, euphoria, and (at high enough doses) respiratory depression. Both of kratom’s key alkaloids preferentially bind to mu-opioid receptors over the other two opioid receptor types, kappa and delta. Mitragynine’s affinity for the mu receptor is about 2.4 times higher than for kappa receptors and nearly 10 times higher than for delta receptors.
So by the receptor-binding definition, kratom’s active compounds function like opioids. This is exactly why the FDA describes kratom as having opioid properties: its alkaloids “bind to the same receptors in the brain (mu opioid receptors) as opioid drugs such as codeine.”
Why It’s Not Quite the Same as Classical Opioids
The critical distinction is that mitragynine acts as a partial agonist at the mu-opioid receptor, meaning it activates the receptor but not to the full extent that morphine or heroin would. Think of it like a dimmer switch turned partway up versus all the way. This partial activation matters most when it comes to one of the deadliest risks of opioid use: respiratory depression, the slowing of breathing that causes most opioid overdose deaths.
Mitragynine does depress breathing, but it has a built-in ceiling effect. The body converts mitragynine into 7-hydroxymitragynine through a specific liver enzyme (CYP3A), and that conversion process saturates at higher doses. Once the enzyme is maxed out, taking more mitragynine doesn’t produce proportionally more of the potent metabolite. Morphine, by contrast, depresses breathing in a straightforward dose-dependent manner: more drug, more suppression, with no built-in brake. Researchers have described this metabolic bottleneck as a possible explanation for kratom’s “improved safety profile” compared to full opioid agonists.
Kratom also does things that traditional opioids don’t. Mitragynine interacts with serotonin, dopamine, and norepinephrine systems in the brain. This broader activity helps explain why low doses feel stimulating rather than sedating, an effect no classical opioid produces.
Dose Changes the Experience
Kratom’s effects shift dramatically depending on how much you take. At lower doses, up to about 5 grams of raw plant material, users report stimulant-like effects comparable to caffeine: increased energy, alertness, and sociability. Between roughly 5 and 15 grams, the opioid-like properties dominate, producing relaxation, pain relief, and sedation. This dose-dependent switch is unusual and reflects kratom’s activity across multiple brain systems, not just opioid receptors.
Dependence and Withdrawal Are Real
One of the clearest parallels between kratom and traditional opioids is withdrawal. Regular users who stop abruptly experience a syndrome that, in the words of researchers from the Journal of Addiction Medicine, “in many respects resembled opioid withdrawal.” Most people who go through it describe the severity as mild to moderate.
In a study of regular users (those taking kratom more than four times per week), the most commonly reported withdrawal symptoms were:
- Anxiety and irritability, each reported by about 33% of regular users
- Low energy and fatigue, reported by roughly 29%
- Difficulty sleeping, reported by about 23%
- Restlessness and body aches, each around 22%
- Nausea and upset stomach, around 20 to 22%
- Depressed mood, reported by about 20%
- Hot and cold flashes, runny nose, watery eyes, reported by 7 to 18%
Severity ratings on a 0 to 100 scale generally landed in the 50 to 70 range for most symptoms, placing them firmly in moderate territory. Intense kratom cravings were rare (about 5% of regular users) but rated nearly 90 out of 100 in severity by those who experienced them. The pattern mirrors classic opioid withdrawal closely enough that some clinicians consider kratom dependence a form of opioid use disorder, though others argue the milder presentation warrants a separate category.
Why People Use It as an Opioid Substitute
A large survey of nearly 3,000 kratom users found that 48% used it primarily for pain relief, 22% for anxiety or depression, 10% for energy and focus, and 10% specifically to reduce opioid use or manage withdrawal. Among those using it as an opioid substitute, over 90% said it was helpful for relieving pain, cutting down on opioid use, and easing withdrawal symptoms.
Animal studies offer some support for this. In lab experiments where rats could self-administer drugs intravenously, mitragynine looked more like saline (inactive) than heroin or morphine in terms of reinforcing behavior. Rats given mitragynine also reduced their subsequent self-administration of heroin and morphine. This lower abuse potential, combined with the ceiling effect on respiratory depression, is why some researchers see kratom alkaloids as potential leads for safer pain medications.
That said, adverse reactions aren’t absent. About 13% of surveyed users reported a bad reaction, though the vast majority described those reactions as mild and self-managed.
Drug Interaction Risks
Kratom’s main alkaloid strongly inhibits a liver enzyme called CYP2D6, which is the same enzyme responsible for metabolizing a wide range of common medications, including certain antidepressants like sertraline (Zoloft), some blood pressure drugs, and many other prescriptions. If you take kratom alongside a medication that relies on CYP2D6 for processing, the drug can build up to higher-than-expected levels in your body. Mitragynine also moderately inhibits another enzyme (CYP2C9) involved in processing anti-inflammatory drugs and blood thinners. These interactions can change how your medications work in unpredictable ways.
The Regulatory Picture
The FDA treats kratom as having opioid properties based on its receptor binding profile and the effects it produces. The agency points to its potential for sedation, nausea, constipation, physical dependence, and respiratory depression. However, kratom is not currently classified as a controlled substance at the federal level in the United States, though several states and municipalities have banned or restricted it independently.
The DEA considered placing kratom on Schedule I in 2016 but backed off after public backlash and calls for more research. So while federal regulators view kratom as pharmacologically opioid-like, it occupies a legal space closer to supplements than to scheduled drugs, sold openly in smoke shops and online with no standardized quality control or dosing guidelines.
The bottom line: kratom is not an opioid in the traditional sense of being derived from or chemically identical to opium compounds. But its active ingredients bind to the same brain receptors, produce overlapping effects, and can cause a withdrawal syndrome that looks a lot like opioid withdrawal. Whether you call it an opioid, an opioid-like substance, or an atypical opioid agonist depends on how strict your definition is. What’s not debatable is that it activates the same system in your brain that opioids do, with real consequences for dependence, withdrawal, and drug interactions.