There are several developing lines of evidence suggesting that brain receptors called GABA-B receptors play a significant role in addiction and its treatment. The investigators wish to examine the sensitivity of brain GABA-B receptors in alcohol and opiate addicts as part of the investigators MRC programme of research in neurotransmitters in alcohol and opiate addiction (NOAA). In this present study the investigators will give 2 different single doses of a drug called baclofen, and a placebo, to 8 healthy male volunteers. This drug affects GABA-B receptors in the central nervous system and is licensed for the treatment of spasticity in people with eg spinal injuries; the investigators are interested in its effects on brain GABA-B receptors. The investigators will measure EEG (brainwaves), eye movements, blood pressure and heart rate, motor co-ordination and subjective effects and also blood levels of the drug in the investigators volunteers before and at intervals after dosing. The investigators will use a double-blind randomised design to minimise expectation effects. The study will provide information on timing and magnitude of effects of baclofen on brain function in healthy subjects so that the investigators can optimise selection and timing of functional measures in future studies of addicts.