Heroin withdrawal typically starts 6 to 24 hours after the last dose. Most people notice the first symptoms closer to the 6- to 12-hour mark, though the exact timing depends on how much you’ve been using, how long you’ve been dependent, and whether the heroin contains other substances like fentanyl. Symptoms peak around 48 to 72 hours and the worst of it usually resolves within 5 to 10 days.
Why Withdrawal Starts So Quickly
Heroin itself breaks down in the body within minutes, with a half-life of just 2 to 6 minutes. But the drug converts into other active compounds (mainly morphine) that linger much longer in the brain. Those compounds are what actually produce the high and, when they clear out, what trigger withdrawal. This is why symptoms don’t hit instantly after the last dose but instead build over several hours as those active byproducts leave the brain.
While you’re using heroin regularly, your brain adjusts to the constant presence of the drug by dialing down its own natural signaling. Neurons that were being suppressed by the drug become primed to fire more intensely once the drug is gone. When heroin clears, those neurons essentially rebound, creating a surge of activity that produces the opposite of heroin’s effects: instead of calm, you get anxiety; instead of pain relief, you get aches; instead of slowed digestion, you get nausea and cramping.
Hour-by-Hour and Day-by-Day Timeline
The first signs usually appear within 6 to 12 hours. These early symptoms feel a lot like a bad flu: watery eyes, runny nose, yawning, sweating, and a growing sense of restlessness. Muscle aches and anxiety tend to set in during this window too. At this stage, the discomfort is mild to moderate, but it escalates quickly.
By 24 to 48 hours, symptoms intensify significantly. This is when nausea, vomiting, diarrhea, and abdominal cramps typically hit hardest. Goosebumps, chills, and rapid heartbeat are common. Sleep becomes extremely difficult. Most people describe this window as the most physically miserable part of the process.
Symptoms peak between 48 and 72 hours after the last dose. After this peak, the acute physical symptoms gradually taper. By day 5 to 7, the worst is usually over, though some people experience lingering physical symptoms for up to 10 days. Sleep problems and mood changes often persist well beyond the acute phase.
What Changes the Timeline
Several factors can shift when withdrawal begins and how intense it gets. Heavier, longer-term use generally leads to earlier onset and more severe symptoms because the brain has adapted more deeply to the drug’s presence. Route of administration matters too. Injecting or smoking heroin delivers it to the brain faster and clears faster, which tends to produce a more rapid onset of withdrawal compared to snorting.
One major complicating factor today is fentanyl. Much of the street heroin supply now contains fentanyl, which is far more potent and has a shorter duration of action. People using fentanyl-laced heroin often develop higher tolerance levels and may use more frequently. This can alter the withdrawal timeline in unpredictable ways and has been linked to higher rates of complications when starting certain medications for treatment.
For comparison, methadone (a longer-acting opioid sometimes used in treatment) has a half-life of 15 to 55 hours, so withdrawal from methadone doesn’t start until 36 to 48 hours after the last dose and can stretch out over 3 to 6 weeks. The shorter the drug’s action, the faster withdrawal hits but the sooner it’s over.
What Acute Withdrawal Feels Like
The physical symptoms get the most attention, but the psychological experience is just as significant. Intense anxiety, irritability, and a powerful craving to use again dominate the first few days. Many people describe a deep sense of dread or hopelessness that makes the physical symptoms feel even worse than they are.
Physically, it’s often compared to a severe stomach flu combined with the worst body aches you’ve ever had. Your body temperature swings between sweating and chills. Pupils dilate. Your legs may feel restless or crampy in a way that makes it impossible to get comfortable. While heroin withdrawal is rarely life-threatening on its own (unlike alcohol or benzodiazepine withdrawal), the dehydration from vomiting and diarrhea can become dangerous if not managed, and the sheer misery of it drives many people back to using before the worst passes.
What Happens After Acute Withdrawal
Once the acute phase ends around day 5 to 10, a second, subtler phase often follows. Known as post-acute withdrawal syndrome, this involves psychological and mood-related symptoms that can persist for months and, in some cases, over a year. The most common lingering symptoms include sleep disruption, anxiety, depression, difficulty concentrating, and irritability. These symptoms tend to fluctuate, coming in waves rather than staying constant, and gradually lessen over time.
The craving to use heroin again can last far longer than any physical symptom. This extended psychological withdrawal is one of the biggest drivers of relapse, which is why treatment guidelines strongly recommend medication-assisted approaches over simply stopping use abruptly. Medications used in treatment work by either activating the same brain receptors at a controlled, steady level or by blocking the effects of opioids if a person does use again. Timing matters with these medications: some need to be started only after withdrawal symptoms are clearly underway, because starting too early can actually trigger a sudden, intense withdrawal episode.
Recognizing the First Signs
If you’re trying to gauge whether withdrawal has started, the earliest reliable signs are yawning, tearing eyes, a runny nose, and restlessness. These might seem minor, but in the context of opioid dependence, they signal that the brain is beginning to react to the absence of the drug. Goosebumps and sweating follow shortly after. Once nausea and muscle aches set in, withdrawal is clearly underway.
Clinicians use a standardized scoring system called the Clinical Opiate Withdrawal Scale to rate severity: scores of 5 to 12 indicate mild withdrawal, 13 to 24 moderate, 25 to 36 moderately severe, and above 36 severe. You don’t need to score yourself, but knowing that withdrawal exists on a spectrum can help set expectations. Not everyone hits severe levels, and the intensity you experience depends on the same factors that influence timing: duration of use, amount used, and the specific substances involved.