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Cover Page - shares
 3 Months Ended
Sep. 30, 2019
Nov. 04, 2019
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q1  
Trading Symbol MEIP  
Entity Registrant Name MEI Pharma, Inc.  
Entity Central Index Key 0001262104  
Current Fiscal Year End Date --06-30  
Entity Filer Category Accelerated Filer  
Entity Current Reporting Status Yes  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Small Business true  
Title of 12(b) Security Common Stock  
Security Exchange Name NASDAQ  
Entity Address, State or Province CA  
Entity Common Stock, Shares Outstanding   73,654,927
Entity Interactive Data Current Yes