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Understanding Impairment: How Long Should You Wait to Drive After Smoking Weed?

01 December 2023

First person point of view of driving a car in traffic

Key Points

  • Smoking cannabis leads to cognitive and psychomotor impairments that can negatively affect driving skills.
  • Marijuana consumption is associated with a higher rate of driving errors and reduced overall performance.
  • The body takes between 30 minutes and two hours to metabolise THC, and impairments in driving can be observed from one to two and a half hours after smoking weed.
  • The appropriate waiting time before driving varies based on factors such as dosage, potency, method of consumption, and individual physiological differences.
  • To ensure safe driving, it is advised to wait a minimum of three to four hours after smoking weed.

Introduction

When it comes to driving under the influence of drugs, the UK government has set certain clear legal limits. According to the Road Traffic Act 1988, it is illegal to operate a motor vehicle while impaired. This includes cannabis, as it can significantly affect one’s cognitive abilities and motor skills necessary for safe driving.

However, determining the exact waiting time for driving after cannabis use is not straightforward. Several factors come into play, including the dosage, method of consumption, individual tolerance, and frequency of use. Due to this reason, the impairing effects of marijuana can vary widely among individuals.

In this blog, we will delve into the topic to provide you with a comprehensive understanding of how long you should wait after smoking weed before driving. We will explore the absorption and elimination of THC, discuss relevant scientific research on the duration of impairment, and examine the legal consequences associated with driving under the influence of cannabis in the UK.

Medical Cannabis Versus Illegal Weed: Why It Matters

The use of marijuana has gained significant attention in recent years, with both medical and recreational purposes being debated and regulated. It’s important to understand this distinction to make informed decisions and navigate the current legal landscape.

Medical Cannabis

Medical marijuana involves using cannabis-derived products that are specifically formulated to provide therapeutic benefits.

  • Legality: In some countries or states, medical weed has been legalised for certain conditions. It is obtained through lawful channels, such as licensed dispensaries or pharmacies, with a doctor’s recommendation or prescription.
  • Regulation and quality control: Medical cannabis is subject to strict regulations to ensure quality and safety. The products go through rigorous testing and are often produced under controlled conditions, ensuring consistent potency and purity.
  • Cannabinoid composition: Medical marijuana products are carefully cultivated and produced to have specific cannabinoid profiles, such as high levels of cannabidiol (CBD) and low levels of delta-9-tetrahydrocannabinol (THC). 
  • Medical use: Medical weed is prescribed or recommended by healthcare professionals to manage symptoms and improve quality of life for various conditions, including chronic pain, epilepsy, multiple sclerosis, nausea and vomiting related to chemotherapy, and many others.

Illegal Weed

Illegal weed, also known as recreational or street cannabis, refers to cannabis obtained and used for non-medical purposes.

  • Legality: In many jurisdictions, the possession, cultivation, and use of recreational cannabis without proper authorisation are still illegal. Engaging in such activities can lead to legal consequences.
  • Uncertain quality: Illicit weed is not subjected to regulated quality control measures, making it difficult to determine its composition, potency, and purity. It may be contaminated with harmful substances, leading to adverse effects.
  • Psychoactive effects: Recreational marijuana typically has higher levels of THC, which can have psychoactive effects, altering perception, mood, and cognition. These properties make it popular for recreational use but may not be suitable for individuals seeking therapeutic benefits without intoxication.
  • Non-medical use: Illegal weed is used primarily for recreational purposes, often for relaxation or social enjoyment. However, it is not prescribed or regulated by healthcare professionals for specific medical conditions.

Medical Cannabis vs. Illegal Weed: A Summary Table 

Medical Cannabis Illegal Weed
Definition Used for medical purposes under medical guidance Used for non-medical/recreational purposes
Legality Legal Generally illegal
Regulation Subject to strict regulations and quality control Lacks regulated quality control measures
Cannabinoid Composition Specific cannabinoid profiles for therapeutic benefits (high CBD, low THC) Higher levels of THC for psychoactive effects
Medical Use Prescribed or recommended by healthcare professionals for specific conditions Not recommended or prescribed by healthcare professionals
Quality and Safety Rigorously tested and produced under controlled conditions for consistent potency and purity Uncertain composition and potential for contaminants
Intoxication Low THC content, minimal psychoactive effects Higher THC content, potential for intoxication
Legal Consequences Legal to possess and use with proper authorisation Possessing or using without legal authorisation can lead to consequences

 

Lyphe: Your Partner for Safe and Legal Medical Marijuana Prescription in the UK

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At Lyphe, we are committed to providing safe and legal medical cannabis prescriptions in the UK. Here’s why you should choose Lyphe:

  • Experienced cannabis doctors: Lyphe is a leading provider of medical cannabis treatments in the UK, boasting the most experienced doctors in this field. We have the expertise necessary to assess your condition and recommend the most suitable treatment for you.
  • Convenient and online: All our appointments are 100% online, allowing you to meet with your doctor, receive prescriptions, and have your medicine delivered right to your door from the comfort of your own home.
  • Dedicated patient support: Our team of patient advisors is committed to assisting and supporting you throughout your treatment journey. They are available to help with booking follow-up appointments, ordering repeat prescriptions, and addressing any concerns or questions you may have.

Interested? Schedule your consultation now with a healthcare specialist at Lyphe for insights into medical cannabis, its benefits for you, and optimal usage methods.

Understanding Cannabis and Its Impact on Driving

A woman seated in the driver's seat of a car with the steering wheel on the left side, shielding her eyes with her hand.

Cannabis use and driving is an important topic that requires understanding to ensure road safety. Here, we will explore the impact of weed on driving abilities and discuss important considerations.

Impairments Caused by Marijuana

Given below are two main types of impairments caused by marijuana consumption:

  • Cognitive Impairments: Cannabis use can impair attention, memory, decision-making, and reaction time, all of which are vital for safe driving.
  • Psychomotor Impairments: Cannabis can affect coordination, motor skills, and perception, leading to difficulties in maintaining proper vehicle control.

Impacts on Driving Performance

A 2021 study published in Frontiers Psychiatry suggests that marijuana use is linked to increased driving errors and decreased performance. The study further concluded that the risk of a vehicle accident increased significantly when cannabis was consumed by the driver. Similarly, another review of literature conducted by the National Academies of Sciences, Engineering, and Medicine also concluded that cannabis use was likely to increase the risk of being involved in a motor vehicle accident.

Aspect of Driving Performance Effects of Marijuana Use
Reaction Time Increased reaction time, leading to delayed responses to unexpected events
Lane Position Increased variability in maintaining a consistent lane position
Speed Control Difficulty in maintaining a steady speed, leading to fluctuations in speed
Divided Attention Reduced ability to attend to multiple tasks simultaneously
Risk Perception Altered perception of risk, resulting in a reduced ability to perceive and respond to potential dangers

How Long After Smoking Cannabis Can You Drive?

When it comes to how long after smoking you can drive, it’s essential to know how fast cannabis can affect your ability to function. While some people may not experience any impairment at all, others may feel the effects of THC from smoking weed almost immediately.

As highlighted above, several factors can influence how long you should wait after smoking cannabis before driving. Let’s delve deeper: 

  • Dosage: The amount consumed can affect the duration of impairment, with higher doses potentially leading to longer-lasting effects.
  • Potency: Products with higher levels of THC may result in longer impairment.
  • Tolerance: Individual tolerance can vary, and frequent users may experience shorter periods of impairment compared to infrequent or first-time users.
  • Metabolism: Variations in metabolism can affect how quickly the body processes and eliminates THC, influencing the length of time one experiences its effects.
  • Route of administration: Different methods of consumption can affect the onset and duration of impairment. Consuming edibles, which have delayed effects, or inhaling higher doses are likely to result in longer periods of altered functioning.
  • Individual differences: Factors unique to each individual, such as body weight, overall health, and sensitivity to the effects of cannabis, can contribute to the duration of impairment.
Time After Inhalation Effect on Driving Ability Notes
20-40 min Peak Impairment Despite decreasing THC blood levels
1-2.5 hours Diminishing Impairment Behavioural impairment starts to diminish
40-100 min (Study) Increased Weaving on Road Significant difference from normal driving
240-300 min (Study) Normal Driving Ability No significant impairment
4-5 hours Self-Felt Impairment, Normal Performance Discrepancy in self-assessment and actual ability

It may take anywhere between 30 minutes and two hours for the body to process the active ingredient in marijuana, THC, despite its levels in the blood decreasing during this period.

A study published in The American Journal of Addiction suggests that behavioural impairment persists for one to two and a half hours after inhalation, even as THC levels in the bloodstream diminish during this period. Consequently, it’s recommended that users wait at least three to four hours before driving.

Another 2020 study published in The Journal of the American Medical Association involved a double-blind, randomised clinical trial where participants inhaled 13.75 mg of THC. Driving performance was measured in a real vehicle and setting.

It was found that participants’ weaving on the road was significantly greater 40–100 minutes after dosing but returned to normal at 240–300 minutes. Moreover, they felt more impaired four to five hours after inhaling THC, although their driving ability (measured by lane position standard deviation) was not significantly altered by then.

CBD and THC Impairment

Ingesting cannabidiol (CBD) along with THC does not substantially reduce THC-induced driving impairment. However, studies show that CBD might affect THC’s pharmacokinetics or alter its behavioural effects.

Furthermore, inhaling high-dose CBD along with THC decreases it in the blood. More specifically, this 2020 finding from the International Medicine Journal suggests that CBD might reduce THC-induced impairment. Inhalation of high-dose CBD alone, however, does not significantly alter THC concentrations.

Legal Implications and Penalties in the UK

A law enforcement officer performing a pat-down on a driver who is standing with his hands on the car's hood.

In the UK, it is illegal to drive if you are impaired by drugs, including weed. The law establishes legal limits for certain controlled substances in the bloodstream while driving. For THC, the active component in marijuana, the limit is two micrograms per litre (µg/L) of blood.

It’s important to note that impairment can occur even below the legal limit, as individual sensitivity to THC varies. Police officers have the authority to conduct roadside impairment tests and, if necessary, request a blood test. Driving under the influence of cannabis can result in severe penalties, including fines, license suspension, and even imprisonment. 

Key Takeaway 

Understanding the effects of cannabis on your driving ability is crucial for ensuring both your safety and that of others on the road. The impairments caused by THC, such as decreased motor skills and cognitive functions, can significantly impact driving performance. Remember, the waiting time before you can drive safely after smoking weed varies based on several factors, including the THC content, your body’s reaction, and the method of consumption. To navigate this safely, we recommend waiting at least three to four hours after smoking. 

For personalised advice and guidance tailored to your specific needs, consider consulting with our experts at Lyphe, the leading medical cannabis clinic in the UK. We can help you make informed decisions about medical marijuana use and driving, ensuring you stay safe and compliant with regulations. 

Book your appointment with Lyphe today and take the first step towards responsible and informed consumption.

References

Arkell TR, Vinckenbosch F, Kevin RC, Theunissen EL, McGregor IS, Ramaekers JG. Effect of cannabidiol and δ9-tetrahydrocannabinol on driving performance: a randomized clinical trial. JAMA. (2020) 324:2177–86. doi: 10.1001/jama.2020.21218

GOV.UK. (n.d.). Drug driving. Retrieved from https://www.gov.uk/drug-driving-law

National Institute on Drug Abuse. (2020). Marijuana: How Does It Affect You?

Pearlson, G. D., Stevens, M. C., & D’Souza, D. C. (2021). Cannabis and driving. Frontiers in Psychiatry, 12. https://doi.org/10.3389/fpsyt.2021.689444

 Sewell RA, Poling J, Sofuoglu M. The effect of cannabis compared with alcohol on driving. Am J Addict. (2009) 18:185–93. doi: 10.1080/10550490902786934

The health effects of cannabis and cannabinoids. (2017). National Academies Press (US). https://doi.org/10.17226/24625

Author: Bojan
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Bojan Ambrus, Head of Marketing & Digital Product at Lyphe Group, is a data-driven growth marketing professional with over 15 years of rich experience. His background includes roles such as Head of Marketing at Vaping.com and growth marketing roles in various enterprises, startups, and scale-ups. His expertise in building and positioning businesses is particularly valuable in the cannabis sector, where he navigates its complexities and regulatory challenges. His strategic marketing insights make Bojan a key player in shaping Lyphe Group's marketing and digital product strategies.

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