Drug problems with a close friend?

Right my best friend has been taking to much acid LSD for his own good and he has been on the stuff like nearly 4 out of 7 in days in the week. He tells me he is suffering with depresion and anexity and paronoid thoughts but he still takes stuff like last night he was wondering around at night at 12 and rung me up to lend him a light for a cig but i didnt know he was wired out of his mind on MDMA COKE and amphetermines i just feel that im gonna lose him as a mate if he goes any furthy i tell him you have to go through your depression to get over your drug problem because he knows its not good to take em but he still does :/ he has recently got him self a girl friend and now she is getting in to the drug seen and yeah i just feel blah what to do can any body tell me how to convince him to just chill out a bit and plus he only 17 many thanks for reading no bad comments i cant be arsed we them kinda people