Friend going through a drug addiction, what should I do?

Okay, first I have a question that needs answered. If my friend were to unsuccesfuly try to commit suicide under the influence of drugs, would they know? And would they send him to rehab or would that be his choice? Also, what are some other choices besides rehabilitation centers to help get over a drug addiction? If you have any additional information, it would be very much appreciated. Thankyou

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