Jordan Duffy's girlfriend died in June several hours after taking a dose of MDMA that he gave her, police say.

Now he has been charged with supplying the drug.

Jordan Duffy, 19, has been charged with drug supply following the death of his girlfriend, Janie Panton Roberts, who allegedly took MDMA. Credit:Facebook

Police say Janie Panton Roberts, 21, and Mr Duffy, 19, a bartender from the Central Coast, went to a music event at the Petersham Inn in Sydney's west on June 4.

Police allege that, at some point, Mr Duffy bought three to four capsules of MDMA.