Coma and seizures can occur following GHB use and when combined with Methamphetamine, there appears to be an increased risk of seizure.  Combining use with other drugs such as alcohol can result in nausea and difficulty breathing.  GHB may also produce withdrawal effects, including insomnia, anxiety, tremors, and sweating.  Other effects of GHB include:  affects consciousness and memory; suppresses respiratory system - lungs may completely stop working; experience similar effects as alcohol, dizziness and drowsiness; depression, hallucinations, and delirium; can cause coma or death, depending on amount used.