Previous studies using transcranial magnetic stimulation (TMS) with paired pulse protocols have shown that a conditioning TMS pulse applied to the human motor cortex changes the excitability of motor pathways from the motor cortex to spinal motorneurons. These effects depended on the stimulus intensity of both conditioning and test pulse and also the ISI). A characteristical sequence of inhibition (short interval cortical inhibition [SICI], GABA-Aerg), facilitation (intracortical facilitation [ICF]), and inhibition again (long interval cortical inhibition [LICI], GABA-Berg) is thought to be physiologically involved in motor control. Previous studies have also shown that neuronal inhibitory motor circuits are also disturbed in ADHD which will be restored by using methylphenidate. In this study the investigators sought to investigate if methamphetamine abuse (from the same chemical class of medications) will alter such effects of methylphenidate.

Design:

Prospective, randomized, -controlled (1:1 randomization), duration-2 single sessions one week apart

Setting:

University psychiatric hospitals in Tehran including Roozbeh Hospital, Rasool Hospital and Imam Hossein General Hospital will refer clients to Iranian National Center for Addiction Studies, Tehran University of Medical Sciences.

Patients:

Fifteen patients with Methamphetamine abuse for at least 2 years plus ADHD are compared with a control group of 15 ADHD patients matched for age and gender

INTERVENTION:

We administer 2 single doses of methylphenidate tablets (10mg) separated by a week interval. A paired pulse protocols will be performed with ten single (unconditioned test pulse) and ten paired TMS pulses (conditioning and test pulse) in an intermixed randomized order.

Short interval cortical inhibition is measured with an Inter-stimulus Intervals (ISI) of 3 msec and a stimulator output of 80% RMT for the conditioning stimulus and 1mVT stimulation intensity for the test stimulus. ICF investigation is measured with an ISI of 13 msec), with the condition of an ISI of 50 msec (ISI 50) and both stimuli applied with 1mVT intensity). Long Interval Cortical Inhibition (LICI) is measured with ISIs of 100 msec (ISI 100), 200 msec (ISI 200), and 300 msec (ISI 300); both stimuli with 1mVT intensity.

Inclusion Criteria:

• DSM-IV diagnosis of Methamphetamine abuse co morbid with ADHD
• Right handedness

Exclusion Criteria:

• Other current Axis I disorders (except simple phobia and nicotine addiction)
• Personal or close family history of seizure disorder
• Ferromagnetic material in body or close to head
• Neurologic disorder
• Pregnancy
• Taking medications known to lower seizure threshold (eg, theophylline)