• Anxiety, depression and insomnia
• Intermittent Tachycardia 
• Tremor
• Risk of seizures
• Confusion, psychosis and delirium
• Excessive Sweating 
• Auditory, tactile, and visual hallucinations 
• Hypertension 
• Nausea and Vomiting 
• Diaphoresis

Onset

• Within 1 to 6 hrs after last dose. 

Duration

• 2 weeks or more.

Little is known about the long-term effects of GHB use but it is possible to become both physically and psychologically dependent on it.

• memory lapses
• drowsiness
• sleep
• dizziness
• headache
• tremor
• decreased body temperature
• decreased blood pressure
• decreased heart rate
• nausea
• diarrhoea
• urinary incontinence

• People who use GHB on a regular basis may become dependent on it.
• They may also develop a tolerance to GHB, which means they will need to use larger amounts to get the same effect.
• Dependence on GHB can be physical, psychological, or both. People who are dependent crave GHB and find it very difficult to stop using it.
• People who are psychologically dependent on GHB may feel an urge to use it when they are in specific situations.
• Physical dependence occurs when a person’s body adapts to GHB and gets used to functioning with GHB present.

• GHB is a naturally occurring metabolite of the inhibitory neurotransmitter GABA; their structures are very similar.
• GHB is a weak agonist at GABA_β receptors (inhibitory), and stimulates the 5-hydroxytryptophan systems and dopamine release; higher concentrations inhibit dopamine release.
• There are ‘GHB receptors’ in the CNS, activation of which increases levels of glutamate (excitatory) in the brain; thus GHB can have both CNS depressant and stimulatory effects.

The drug is rapidly absorbed orally, with an onset of action within 15 minutes. Roughly 95 percent of GHB is metabolized in the liver, and it’s half-life ranges from 30 to 60 minutes. Only five percent of the parent drug is excreted via the kidneys. Detection of GHB in the urine may be difficult after 24 hours due to it’s short half-life

http://www.drugs.com/ghb.html

• GHB is generally swallowed or snorted although some individuals inject it.
• The effects of any drug also depend on the amount taken. This can be very hard to judge as the quality and strength of drugs can vary greatly from one batch to another. This is a particular concern with GHB, as there can be a very small difference between the dose required for a “high” and an overdose.
• The immediate effects of GHB may start to be felt within 15-20 minutes and last for approximately 3-4 hours.