THC impairs motor function for several hours after use, slowing reaction time and weakening coordination and the ability to track a moving target, which is why cannabis raises crash risk. Its effect on pain is more subtle: in lab studies it makes pain feel more tolerable and less unpleasant more than it lowers pain intensity, and in patients with chronic pain the benefit is real but small.
Both effects run through the same place. CB1 cannabinoid receptors sit in brain areas that control movement and in the pathways that carry and interpret pain signals. This article covers what controlled studies show about cannabis and motor skills, including driving, and what clinical trials show about pain, starting with the British surgical study that first appeared on this page.
Evidence at a Glance
| Claim | Evidence level | Source |
|---|---|---|
| Cannabis use is linked to increased motor vehicle crash risk | Substantial | National Academies, 2017 |
| THC impairs tracking, reaction time, divided attention and lane position | Strong (controlled experiments) | Hartman and Huestis, 2013 |
| Frequent users show less, but not zero, motor impairment | Moderate | Desrosiers et al., 2015 |
| Cannabinoids raise pain threshold and tolerance and reduce pain unpleasantness in healthy adults | Moderate (meta-analysis, small effects) | De Vita et al., 2018 |
| Cannabinoids reduce chronic pain in adults | Substantial, but benefits are small | National Academies; Wang et al., BMJ, 2021 |
| THC-dominant medicines give 50% relief of nerve pain | No clear evidence (very low certainty) | Cochrane, 2026 |
How Cannabis Affects Motor Function
NIDA lists impaired body movement among the short-term effects of cannabis. The reason is anatomical. Reviews of brain imaging research identify the cerebellum, which coordinates movement and balance, as one of the regions rich in cannabinoid receptors. Animal research shows how central those receptors are: in mice bred without CB1 receptors, THC’s usual effects of frozen posture, reduced movement and lower body temperature disappeared entirely.
What lab tests show
A review by NIDA researchers Rebecca Hartman and Marilyn Huestis summarized decades of controlled studies. After smoking cannabis, people showed impairment on critical tracking tests, reaction time, divided-attention tasks and lane-position variability. Drivers tried to compensate by slowing down, but control broke down as tasks became more complex. Combining cannabis with alcohol made impairment worse, especially lane weaving.
Does tolerance protect regular users?
Partly. In a NIDA study, 14 frequent and 11 occasional smokers each smoked a 6.8% THC cigarette under supervision. Occasional smokers had significantly more trouble with tracking tasks and divided attention, but frequent smokers were still impaired. Hartman and Huestis likewise found that despite tolerance in frequent smokers, complex tasks still showed impairment.
How long it lasts
Impairment tracks the high. Inhaled THC peaks in the blood within 2 to 10 minutes, while edibles peak 1 to 6 hours after eating, so impairment from edibles starts later and can last longer. In the NIDA tolerance study, testing ran out to 22.5 hours after smoking to capture the full time course.
Cannabis and Driving
The National Academies found substantial evidence that cannabis use is linked to increased motor vehicle crash risk. How large is the risk? Estimates differ:
- Hartman and Huestis reported that epidemiologic data show crash risk roughly doubles after smoking cannabis (studies relying on urine tests found no link), and that blood THC of 2 to 5 ng/mL is associated with substantial impairment, especially in occasional users.
- A 2019 meta-analysis of 13 culpability studies estimated a smaller average increase in crash risk of about 1.28 times, and argued that earlier figures were exaggerated by how they were interpreted.
Either way, the risk is real and adds up when combined with alcohol. In Washington, 5 ng/mL of active THC in the blood within two hours of driving is a per se DUI; see our Washington marijuana laws and Oregon marijuana laws guides. The safest rule is simple: if you feel any effect, do not drive.
How Cannabis Affects Pain Sensitivity
Pain in healthy volunteers
Lab studies apply controlled pain, such as heat or pressure, to healthy people. A 2018 meta-analysis of 18 placebo-controlled studies with 442 participants found that cannabinoids produced small increases in pain threshold and pain tolerance and a small to medium drop in how unpleasant pain felt. They did not reliably reduce how intense the pain was. The authors suggested cannabis may change how people feel about pain more than the pain signal itself, which may explain why many users say cannabis helps.
How it works
NCI explains that cannabinoids affect pain through supraspinal, spinal and peripheral actions, acting on both the pathways that carry pain signals up to the brain and those that dampen them on the way down, and possibly through anti-inflammatory effects. CB1 receptors are also increased in brain regions that process pain.
The surgical pain study
The study that originally appeared on this page was led by Dr. Anita Holdcroft at Imperial College London and published in Anesthesiology in 2006. Patients recovering from surgery received a single oral dose of Cannador, a cannabis plant extract, at 5, 10 or 15 mg. The share who needed rescue pain medication fell with dose: all 11 patients at 5 mg, half of 30 at 10 mg, and a quarter of 24 at 15 mg. Pain at rest also fell with dose, but sedation and other side effects rose, and the trial was stopped after a serious fainting-type (vasovagal) event in a patient on 15 mg. It was a small dose-finding study without a placebo group.
Chronic pain in patients
- The National Academies found substantial evidence that cannabis or cannabinoids are effective for chronic pain in adults.
- A 2021 BMJ meta-analysis of 32 trials with 5,174 patients found non-inhaled medical cannabis produced small to very small improvements in pain, physical function and sleep, with more dizziness, drowsiness and nausea.
- A companion guideline issued a weak recommendation to offer a trial of non-inhaled cannabis when standard care is not enough.
- For nerve pain, the 2026 Cochrane update of 21 trials found no clear evidence that THC-dominant medicines deliver 50% pain relief, and THC/CBD-balanced products produced gains the authors judged not clinically relevant.
Risks and Side Effects
- Slowed reactions, poor coordination and higher crash risk
- Dizziness and poor coordination that can raise the risk of falls
- Dizziness, drowsiness, nausea and impaired attention in pain trials
- Rapid heart rate and low blood pressure, listed by NCI among adverse effects
- Dependence with regular use; see marijuana addiction
Talk to Your Doctor
If you are considering cannabis for pain, discuss it with your doctor, especially if you take opioids, sedatives, sleep aids or blood thinners, or have heart disease or balance problems. Ask about dose, timing and when it is safe to drive. Our cannabis dosage guide explains how THC milligrams and onset times work.
Motor Function and Pain Sensitivity FAQ
Does marijuana affect coordination?
Yes. THC impairs tracking, reaction time and divided attention for several hours after use, and complex tasks like driving remain impaired even in frequent users who have built some tolerance.
How long after smoking weed are you impaired?
Smoked THC peaks within minutes and the strongest impairment lasts a few hours. Edibles start later and last longer. Researchers have tracked effects in some tasks for many hours, so wait well beyond the high before driving.
Does marijuana raise or lower your pain tolerance?
In lab studies of healthy adults, cannabinoids slightly raised pain threshold and tolerance and made pain feel less unpleasant, without reliably lowering pain intensity.
Does marijuana help with pain?
For chronic pain, research shows a real but small benefit on average. For nerve pain, a 2026 Cochrane review found no clear evidence of major relief from THC-dominant medicines.
Is it safe to drive after using cannabis?
No, not while you feel any effect. The National Academies found substantial evidence linking cannabis use to motor vehicle crashes, and Washington treats 5 ng/mL of active THC in the blood as a DUI.
Why does cannabis make people move less?
THC acts on CB1 receptors in movement-control areas such as the cerebellum. In mice, THC’s effects of reduced movement and frozen posture vanish when CB1 receptors are removed.
More explainers are in our Cannabis Health & Research section, including cannabis and the central nervous system.
For adults 21+ in legal states. General information, not medical advice. Talk to a doctor before using cannabis for a health condition.