Using speed type drugs can make you want to drink more alcohol but it can also mask alcohol’s effects – so you get very drunk without realising it. 

The hallucinogens among the stimulant family like Ecstasy distort perception and mood in ways obviously very dangerous for driving. Which is why studies like NZ's IDMS typically find that most ecstasy users avoid driving.

Driving when you’re "coming down" is also very dangerous as with alcohol hang-overs. When the effects of stimulants are waning and one is sleep deprived  driving is badly affected. You may nod off at the wheel. Antihistamines etc up effects. 

See left sidebar for more info about the effects

Driving after amphetamines

Never drive after recent heavy use. Ensure you have had several hours sleep between last high and driving. Intoxication will be at unsafe levels for at least 12 hours (very in first 7) and up to 24 after heavy use. Judgment will be impaired and risk-taking likely. When a "sleep debt" is too high an intoxicated driver may feel alert but unknowingly experience "micro sleeps". 

Micro-sleeps or drowsiness may occur when one who is "coming down" from long wakefulness feels fatigued even when the drug has nearly exited or has gone from the body. Driving may be affected in a variety of ways for as long as 4 weeks after use due to after-effects of depression, exhaustion,  mood swings and possibly hallucinations or false persecutory beliefs.

         Slows your reaction times if you are intolerant or use extra to get high or inject IV.

         Can make you lose your balance, coordination (if intoxicated) and concentration or get confused.

         Shifts attention inward and away from what’s happening on the road, affects judgment.

         Gives blurry tunnel vision & altered visual depth perception, overconfidence.

See medications page for rough  time after use to drive "clock". 

Driving when you’re hanging out or going through withdrawal (noddy / shirty) is also dangerous. 

Combining alcohol or pot and opiates multiplies the depressant effects of both drugs, even if only small quantities are used. You feel sleepy & uncoordinated and have a higher risk of a serious crash. 

Methadone plus benzodiazepines even long after dosing gives a heroin like high - highly dangerous 

In W.A. opiate users at <1% of us are present at 30% of fatal crashes Of the drug drivers Darke interviewed 1/3rd reported involvement in a drug driving crash. Heroin was the drug involved in 53% of them, cannabis in 46% and alcohol factored in 42% of the crashes.

Cannabis - commonest drug detected in erratic drivers

Smoking joints or bongs reduces your ability to control a vehicle and drive safely; 1 joint is like being at the alcohol limit in risk for around 2 hours Other use like hash (a class B cannabis product) and skunk is even riskier, and after eating weed the effects can last 24 hours

You often don’t realise your driving is affected until you’re faced with an unexpected situation. Its only then you find you can’t act decisively (if you're still awake). Miss or misread signs, poor curve taking

Using cannabis plus alcohol or other depressants greatly multiplies ill impacts of each substance like slowed reactions & in-coordination (affects steering), even if you using just a little. 100x crash risk

 

Using Cannabis with amphetamines can raise heart rate and blood pressure causing wooziness. Mixing with other stimulants eg cocaine or caffeine has unpredictable effects -  consciousness level may fluctuate 

 

See right sidebar for more info about the effects

 

Driving can be unsafe for 3-5 hours after smoking (it's individual) and 24 hours after eating it. Some users may be quite affected until 7 hours after smoking. A good part of a joint takes you to the equivalent of "over the limit" in impairment. 

 

Hashish / oil or resin in small measure brings marked impairment in following road signs and tracking / positioning on road. A French study and that of Menetrey et al suggest tolerance is no protection from impairment and crashes. 

 

Since remnant effects of cannabis linger for 24 hours so users might plan their schedule not to drive early morning or late night when biorhythms naturally increase tiredness and may exacerbate any residual drowsiness.

 

It is good to nap in between use and driving. Avoid combining use with alcohol or other psycho-active drugs. They enhance and speed impact of all the detrimental effects.

 

You can be at half the alcohol limit but equal to double the limit in driving impairment (Ramaekers). Sudden head movements / jerks co-relate to cannabic driving impairment  so look out for these when assessing your fitness. 

Drowsy, distractable, long closure blinks and inco-ordination lead to reduced vigilance and scanning and slowed reactions

 Visual effects, and unable to read signs leads to weaving and lost drivers making coarse steering reversals

Confusion and "black outs" (no later memory of trip sector as not really conscious) cause poor journey planning

Effects are increased by the use of most other depresant drugs including alcohol.