• Assess the antidepressant/anxiolytic effect of creatine in male and female methamphetamine users
• Assess creatine's effect on methamphetamine use
• Assess the safety of creatine in male methamphetamine users with depression

Inclusion Criteria:

• Current primary diagnosis of methamphetamine dependence or abuse, with methamphetamine preferred drug of abuse
• Current diagnosis of major depressive disorder (primary or substance-induced)
• Current diagnosis of an anxiety disorder (primary or substance-induced)
• Current Hamilton Depression Rating scale score > or = to 16
• Current Hamilton Anxiety Scale score > = to 18
• If taking a psychotropic medication for depressed or anxious mood, regimen must be stable for > = to 4 weeks prior to creatine treatment initiation

Exclusion Criteria:

• Persons unable to provide adequate informed consent
• Persons who are at clinically significant suicidal or homicidal risk
• Primary substance-related diagnosis other than methamphetamine dependence or abuse
• Positive pregnancy test (females only)
• History of renal disease
• Clinically significant medical or neurological illness identified by history, physical exam and laboratory testing
• History of hypersensitivity reaction to creatine