A company not hiring back a recovering drug addict?

Hey guys a friend of mine used to work for this company with me. He was on doctor prescribed drugs to help with a drug addiction. One day he came to work very drowsy from the drugs he was taking. Now let me be clear he was not abusing these drugs he was taking them as prescribed and the company told him he was not allowed to work until he provided information documenting the drugs were prescribed. So he did just that and found that the drugs he was prescribed had side-effects when mixed with the others he was taking. He applied back to work there again because when he was trying to find his info they erased his info and all that stuff. By law can the company not hire him back? He has sufficient proof is he covered under the ADA in regards to his drug addiction and rehabilitation?

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